Halderman ch076 lecture

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  • Figure 76-1 Many oxygen sensors are located in the exhaust manifold near its outlet so that the sensor can detect the presence or absence of oxygen in the exhaust stream for all cylinders that feed into the manifold.
  • Figure 76-2 (a) When the exhaust is lean, the output of a zirconia oxygen sensor is below 450 mV.
  • Figure 76-2 (b) When the exhaust is rich, the output of a zirconia oxygen sensor is above 450 mV.
  • Figure 76-3 Most conventional zirconia oxygen sensors and some wide-band oxygen sensors use the cup (finger) type of design.
  • Figure 76-4 A typical heated zirconia oxygen sensor, showing the sensor signal circuit that uses the outer (exhaust) electrode as the negative and the ambient air side electrode as the positive.
  • Figure 76-5 The oxygen sensor provides a quick response at the stoichiometric air-fuel ratio of 14.7:1.
  • Figure 76-8 Testing an oxygen sensor using a DMM set on DC volts. With the engine operating in closed loop, the oxygen voltage should read over 800 mV and lower than 200 mV and be constantly fluctuating.
  • Figure 76-9 Using a digital multimeter to test an oxygen sensor using the MIN/MAX record function of the meter.
  • CHART 76–1 The test results of using a digital meter set to read minimum and maximum values while testing a narrow-band oxygen sensor. * Check for an exhaust leak upstream from the O2S or ignition misfire that can cause a false lean indication before further diagnosis.
  • Figure 76-10 Connecting a handheld digital storage oscilloscope to an oxygen sensor signal wire. Check the instructions for the scope as some require the use of a filter to be installed in the test lead to reduce electromagnetic interference that can affect the oxygen sensor waveform.
  • Figure 76-11 The waveform of a good oxygen sensor as displayed on a digital storage oscilloscope (DSO). Note that the maximum reading is above 800 mV and the minimum reading is less than 200 mV.
  • Figure 76-12 The post catalytic converter oxygen sensor should display very little activity if the catalytic converter is efficient.
  • Figure 76-13 A conventional zirconia oxygen sensor can only reset to exhaust mixtures that are richer or leaner than 14.7:1 (lambda 1.00).
  • Figure 76-14 A planar design zirconia oxygen sensor places all of the elements together, which allows the sensor to reach operating temperature quickly.
  • Figure 76-15 The reference electrodes are shared by the Nernst cell and the pump cell.
  • Figure 76-16 When the exhaust is rich, the PCM applies a negative current into the pump cell.
  • Figure 76-17 When the exhaust is lean, the PCM applies a positive current into the pump cell.
  • CHART 76–2 A comparison showing what a factory scan tool and a generic OBD-II scan tool might display at various air-fuel ratios.
  • Figure 76-18 Testing a dual cell wide-band oxygen sensor can be done using a voltmeter or a scope. The meter reading is attached to the Nernst cell and should read stoichiometric (450 mV) at all times. The scope is showing activity to the pump cell with commands from the PCM to keep the Nernst cell at 14.7:1 air-fuel ratio.
  • Figure 76-19 A single cell wide-band oxygen sensor has four wires with two for the heater and two for the sensor itself. The voltage applied to the sensor is 0.4 V (3.3 − 2.9 = 0.4) across the two leads of the sensor.
  • Halderman ch076 lecture

    1. 1. OXYGEN SENSORS 76
    2. 2. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Prepare for ASE Engine Performance (A8) certification test content area “E” (Computerized Engine Controls Diagnosis and Repair). </li></ul></ul><ul><ul><li>Discuss how oxygen sensors (O2S) work. </li></ul></ul><ul><ul><li>List the methods that can be used to test oxygen sensors. </li></ul></ul>
    3. 3. Objectives <ul><li>The student should be able to: </li></ul><ul><ul><li>Describe how a wide-band oxygen sensor works. </li></ul></ul><ul><ul><li>List how to test narrow- and wide-band oxygen sensors. </li></ul></ul>
    4. 4. OXYGEN SENSORS
    5. 5. Oxygen Sensors <ul><li>Purpose and Function </li></ul><ul><ul><li>Sensors in the exhaust system measure oxygen content </li></ul></ul><ul><ul><li>These are oxygen sensors (O2S) </li></ul></ul>
    6. 6. Figure 76-1 Many oxygen sensors are located in the exhaust manifold near its outlet so that the sensor can detect the presence or absence of oxygen in the exhaust stream for all cylinders that feed into the manifold.
    7. 7. Oxygen Sensors <ul><li>Purpose and Function </li></ul><ul><ul><li>Oxygen sensors are installed in exhaust manifold or the exhaust pipe </li></ul></ul><ul><ul><li>Sensor monitors oxygen levels in exhaust stream and ambient air </li></ul></ul>
    8. 8. Oxygen Sensors <ul><li>Purpose and Function </li></ul><ul><ul><li>Zirconia oxygen sensor is made of zirconium dioxide (ZrO 2 ) </li></ul></ul><ul><ul><li>ZrO 2 is electrically conductive and can generate small voltage in presence of oxygen </li></ul></ul>
    9. 9. Oxygen Sensors <ul><li>Narrow Band </li></ul><ul><ul><li>Conventional zirconia oxygen sensor only detects if exhaust is richer or leaner than 14.7:1 </li></ul></ul>
    10. 10. Oxygen Sensors <ul><li>Narrow Band </li></ul><ul><ul><li>O2S referred to as: </li></ul></ul><ul><ul><ul><li>Two-step sensor which is either rich or lean </li></ul></ul></ul><ul><ul><ul><li>Narrow-band sensor that informs PCM whether exhaust is rich or lean </li></ul></ul></ul>
    11. 11. Oxygen Sensors <ul><li>Narrow Band </li></ul><ul><ul><li>Voltage value where zirconia oxygen sensor switches from rich to lean or lean to rich is 0.45 V (450 mV) </li></ul></ul><ul><ul><ul><li>Above 0.45 V = rich </li></ul></ul></ul><ul><ul><ul><li>Below 0.45 V = lean </li></ul></ul></ul>
    12. 12. Figure 76-2 (a) When the exhaust is lean, the output of a zirconia oxygen sensor is below 450 mV.
    13. 13. Figure 76-2 (b) When the exhaust is rich, the output of a zirconia oxygen sensor is above 450 mV.
    14. 14. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Zirconia oxygen sensor sensing element is in shape of thimble </li></ul></ul><ul><ul><li>It is referred to as: </li></ul></ul><ul><ul><ul><li>Thimble design </li></ul></ul></ul>
    15. 15. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>It is referred to as: </li></ul></ul><ul><ul><ul><li>Cup design </li></ul></ul></ul><ul><ul><ul><li>Finger design </li></ul></ul></ul>
    16. 16. Figure 76-3 Most conventional zirconia oxygen sensors and some wide-band oxygen sensors use the cup (finger) type of design.
    17. 17. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Zirconia oxygen sensor has heater inside thimble </li></ul></ul><ul><ul><li>Sensor similar to battery with two electrodes and an electrolyte </li></ul></ul>
    18. 18. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Electrolyte is zirconia and is solid </li></ul></ul><ul><ul><li>Two porous platinum electrodes with these functions </li></ul></ul><ul><ul><ul><li>Exhaust side electrode exposed to exhaust stream </li></ul></ul></ul>
    19. 19. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Two porous platinum electrodes with these functions </li></ul></ul><ul><ul><ul><li>Ambient side electrode exposed to outside air </li></ul></ul></ul><ul><ul><ul><li>Ambient electrode is the signal electrode, or reference electrode </li></ul></ul></ul>
    20. 20. Figure 76-4 A typical heated zirconia oxygen sensor, showing the sensor signal circuit that uses the outer (exhaust) electrode as the negative and the ambient air side electrode as the positive.
    21. 21. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Electrolyte (zirconia) conducts electrodes as follows: </li></ul></ul><ul><ul><ul><li>If exhaust is rich, O 2 from reference electrode wants to flow to exhaust electrode, which generates voltage </li></ul></ul></ul>
    22. 22. Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Electrolyte (zirconia) conducts electrodes as follows: </li></ul></ul><ul><ul><ul><li>If exhaust is lean, O 2 flow is not needed and no voltage is produced </li></ul></ul></ul>
    23. 23. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Exhaust passes through end of sensor </li></ul></ul><ul><ul><li>Exhaust gases contact outer side of thimble </li></ul></ul>
    24. 24. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Atmospheric air enters other end of sensor or through wire </li></ul></ul><ul><ul><li>Air contacts inner side of thimble </li></ul></ul>
    25. 25. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Inner surface becomes negative electrode </li></ul></ul><ul><ul><li>Outer surface becomes positive electrode </li></ul></ul>
    26. 26. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Exhaust from rich air-fuel mixture contains little oxygen </li></ul></ul><ul><ul><li>Exhaust from lean air-fuel mixture contains more oxygen </li></ul></ul>
    27. 27. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Negatively charged oxygen ions are drawn to thimble and collect on inner and outer surfaces </li></ul></ul><ul><ul><li>Oxygen in atmosphere exceeds that in exhaust gases, air side of thimble draws more negative oxygen ions than exhaust side </li></ul></ul>
    28. 28. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Difference between two sides generates voltage </li></ul></ul><ul><ul><li>When concentration of oxygen on exhaust side is low, a high voltage is generated </li></ul></ul>
    29. 29. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>As oxygen concentration on exhaust side increases, voltage drops </li></ul></ul><ul><ul><li>An O2S does not send voltage signal until its tip reaches a temperature of about 572°F (300°C) </li></ul></ul>
    30. 30. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>If exhaust contains very little oxygen, PCM assumes intake charge is rich and reduces fuel delivery </li></ul></ul>
    31. 31. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>When oxygen level is high, PCM assumes intake charge is lean and increases fuel delivery </li></ul></ul>
    32. 32. Figure 76-5 The oxygen sensor provides a quick response at the stoichiometric air-fuel ratio of 14.7:1.
    33. 33. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>One-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Single wire is the O2S signal wire </li></ul></ul></ul></ul>
    34. 34. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>One-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Ground is through shell and threads of sensor and through exhaust manifold </li></ul></ul></ul></ul>
    35. 35. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Two-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Has signal wire and ground wire </li></ul></ul></ul></ul>
    36. 36. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Three-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Uses electric resistance heater to help O2S get up to temperature more quickly and keep sensor at operating temperature even when at idle </li></ul></ul></ul></ul>
    37. 37. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Three-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Wires for signal, power, and ground </li></ul></ul></ul></ul>
    38. 38. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Four-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>A heated O2S (HO2S) </li></ul></ul></ul></ul>
    39. 39. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Four-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Uses signal wire and signal ground </li></ul></ul></ul></ul>
    40. 40. Oxygen Sensors <ul><li>Operation </li></ul><ul><ul><li>Designs for oxygen sensors: </li></ul></ul><ul><ul><ul><li>Four-wire oxygen sensor </li></ul></ul></ul><ul><ul><ul><ul><li>Other two wires are power and ground for heater </li></ul></ul></ul></ul>
    41. 41. Oxygen Sensors <ul><li>Heater Circuits </li></ul><ul><ul><li>Heater circuit on oxygen sensors requires 0.8 to 2.0 amperes </li></ul></ul><ul><ul><li>Heater keeps sensor at about 600°F (315°C) </li></ul></ul>
    42. 42. Oxygen Sensors <ul><li>Heater Circuits </li></ul><ul><ul><li>Wide-band oxygen sensor operates at higher temperature </li></ul></ul><ul><ul><li>1,200°F to 1,400°F (650°C to 760°C) </li></ul></ul><ul><ul><li>Wide-band oxygen sensor requires 8 to 10 amperes </li></ul></ul>
    43. 43. TITANIA OXYGEN SENSOR
    44. 44. Titania Oxygen Sensor <ul><li>Titania (titanium dioxide) oxygen sensor does not produce voltage </li></ul><ul><li>It changes resistance due to presence of oxygen in exhaust </li></ul><ul><li>Titania oxygen sensors use four-terminal variable resistance unit with heating element </li></ul>
    45. 45. Titania Oxygen Sensor <ul><li>Samples exhaust air only and uses reference voltage from PCM </li></ul><ul><li>Uses 14 mm thread </li></ul><ul><li>Not interchangeable with zirconia oxygen sensors, which use 18 mm thread </li></ul>
    46. 46. Titania Oxygen Sensor <ul><li>Changing resistance of titania oxygen sensor changes voltage of sensor circuit </li></ul><ul><li>Voltage signal is above 450 mV when exhaust is rich </li></ul><ul><li>Voltage is low (below 450 mV) when exhaust is lean </li></ul>?
    47. 47. PCM USES OF THE OXYGEN SENSOR
    48. 48. PCM Uses of the Oxygen Sensor <ul><li>Fuel Control </li></ul><ul><ul><li>Amount of oxygen delivered to an engine is determined by the powertrain control module (PCM) </li></ul></ul>
    49. 49. PCM Uses of the Oxygen Sensor <ul><li>Fuel Control </li></ul><ul><ul><li>On engine start-up, oxygen sensor is cold and cannot supply rich and lean signals </li></ul></ul>
    50. 50. PCM Uses of the Oxygen Sensor <ul><li>Fuel Control </li></ul><ul><ul><li>PCM determines mixture based on inputs from engine coolant temperature, throttle position sensor, and others until oxygen sensor can supply usable signal </li></ul></ul>
    51. 51. PCM Uses of the Oxygen Sensor <ul><li>Fuel Control </li></ul><ul><ul><li>When only PCM determines fuel needed it is called open-loop operation </li></ul></ul><ul><ul><li>When O2S supplies rich and lean signals, PCM fine-tunes correct air-fuel mixture </li></ul></ul>
    52. 52. PCM Uses of the Oxygen Sensor <ul><li>Fuel Control </li></ul><ul><ul><li>Upstream oxygen sensors give data for fuel control </li></ul></ul><ul><ul><li>System now operates in closed loop </li></ul></ul>
    53. 53. PCM Uses of the Oxygen Sensor <ul><li>Fuel Trim </li></ul><ul><ul><li>Fuel trim numbers determined from signals from oxygen sensor(s) </li></ul></ul><ul><ul><li>If engine is operating on too lean an air-fuel mixture, PCM can cause an increase in the commanded injector pulse width to bring air-fuel mixture to proper range </li></ul></ul>?
    54. 54. OXYGEN SENSOR DIAGNOSIS
    55. 55. Oxygen Sensor Diagnosis <ul><li>PCM System Tests </li></ul><ul><ul><li>Oxygen sensors are used for diagnosis of other systems and components </li></ul></ul><ul><ul><li>If fault develops with oxygen sensor, PCM may not be able to rest other systems </li></ul></ul>
    56. 56. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>When oxygen sensor is replaced, inspect old sensor to determine cause of failure </li></ul></ul><ul><ul><li>If cause is not discovered, another sensor could fail </li></ul></ul>
    57. 57. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>Black sooty deposits indicating rich air-fuel mixture </li></ul></ul></ul>
    58. 58. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>White chalky deposits </li></ul></ul></ul><ul><ul><ul><ul><li>Characteristic of silica contamination </li></ul></ul></ul></ul>
    59. 59. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>White chalky deposits </li></ul></ul></ul><ul><ul><ul><ul><li>Usual causes: silica deposits in fuel or technician using wrong type silicone sealant </li></ul></ul></ul></ul>
    60. 60. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>White sandy or gritty deposits </li></ul></ul></ul><ul><ul><ul><ul><li>Characteristic of antifreeze contamination </li></ul></ul></ul></ul>
    61. 61. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>White sandy or gritty deposits </li></ul></ul></ul><ul><ul><ul><ul><li>Defective cylinder head or intake manifold gasket could be cause </li></ul></ul></ul></ul>
    62. 62. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>White sandy or gritty deposits </li></ul></ul></ul><ul><ul><ul><ul><li>Antifreeze may also leave oxygen sensor green </li></ul></ul></ul></ul>
    63. 63. Oxygen Sensor Diagnosis <ul><li>Visual Inspection </li></ul><ul><ul><li>Inspection may reveal the following: </li></ul></ul><ul><ul><ul><li>Dark brown deposits indicate excessive oil consumption </li></ul></ul></ul><ul><ul><ul><ul><li>Possible causes: defective positive crankcase ventilation system or mechanical engine problem such as defective valve stem seals or piston rings </li></ul></ul></ul></ul>
    64. 64. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>With engine off, connect red lead of meter to oxygen sensor signal wire </li></ul></ul></ul><ul><ul><ul><ul><li>Connect black meter lead to good engine ground </li></ul></ul></ul></ul>
    65. 65. Figure 76-8 Testing an oxygen sensor using a DMM set on DC volts. With the engine operating in closed loop, the oxygen voltage should read over 800 mV and lower than 200 mV and be constantly fluctuating.
    66. 66. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>Start engine and allow it to reach closed-loop operation </li></ul></ul></ul>
    67. 67. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>If oxygen sensor fails to respond; voltage remains about 450 mV </li></ul></ul></ul></ul></ul>
    68. 68. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Sensor may be defective </li></ul></ul></ul></ul></ul>
    69. 69. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Before replacing oxygen sensor, check manufacturer’s recommended procedures </li></ul></ul></ul></ul></ul>
    70. 70. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>If oxygen sensor reads high all the time (above 550 mV) </li></ul></ul></ul></ul></ul>
    71. 71. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Fuel system could be supplying too rich a fuel mixture </li></ul></ul></ul></ul></ul>
    72. 72. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Digital high-impedance voltmeter can be used to check oxygen sensor </li></ul></ul><ul><ul><ul><li>In closed-loop operation, oxygen sensor voltage should be constantly changing as fuel mixture is being controlled </li></ul></ul></ul><ul><ul><ul><ul><li>Results should be interpreted as follows: </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Oxygen sensor could be contaminated </li></ul></ul></ul></ul></ul>
    73. 73. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>When O2S reads high for reasons beside rich mixture it is false rich indication </li></ul></ul>
    74. 74. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>False rich indication can be attributed to: </li></ul></ul><ul><ul><ul><li>Contaminated O2S due to additives in engine coolant or silicon poisonings </li></ul></ul></ul>
    75. 75. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>False rich indication can be attributed to: </li></ul></ul><ul><ul><ul><li>EGR valve that is stuck open </li></ul></ul></ul>
    76. 76. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>False rich indication can be attributed to: </li></ul></ul><ul><ul><ul><li>Spark plug wire too close to oxygen signal wire inducing excessive voltage </li></ul></ul></ul>
    77. 77. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>False rich indication can be attributed to: </li></ul></ul><ul><ul><ul><li>Loose oxygen sensor ground connection </li></ul></ul></ul><ul><ul><ul><li>Break or contamination of wiring and connectors </li></ul></ul></ul>
    78. 78. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>If oxygen sensor voltage remains low (below 350 mV) oxygen sensor could be bad </li></ul></ul><ul><ul><ul><li>Check for vacuum leak or clogged fuel injector(s) </li></ul></ul></ul>
    79. 79. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>If oxygen sensor reads low for reason besides lean mixture, it is called false lean indication </li></ul></ul>
    80. 80. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>False lean indications can be contributed to: </li></ul></ul><ul><ul><ul><li>Spark plug misfire </li></ul></ul></ul><ul><ul><ul><li>Ignition misfires—check for defective spark plug wire, spark plug and so forth </li></ul></ul></ul>
    81. 81. Oxygen Sensor Diagnosis <ul><li>Digital Voltmeter Testing </li></ul><ul><ul><li>Exhaust leak in front of O2S </li></ul></ul><ul><ul><ul><li>Exhaust leak can cause outside oxygen to be drawn into the exhaust past O2S </li></ul></ul></ul>?
    82. 82. Oxygen Sensor Diagnosis <ul><li>Min/Max Testing </li></ul><ul><ul><li>Digital meter set on DC volts can record the minimum and maximum voltage with engine running </li></ul></ul>
    83. 83. Oxygen Sensor Diagnosis <ul><li>Min/Max Testing </li></ul><ul><ul><li>Values for good oxygen sensor </li></ul></ul><ul><ul><ul><li>Minimum value of less than 300 mV </li></ul></ul></ul><ul><ul><ul><li>Maximum value above 800 mV </li></ul></ul></ul>
    84. 84. Figure 76-9 Using a digital multimeter to test an oxygen sensor using the MIN/MAX record function of the meter.
    85. 85. Oxygen Sensor Diagnosis <ul><li>Min/Max Testing </li></ul><ul><ul><li>Replace oxygen that fails to go below 300 mV or above 700 mV </li></ul></ul>
    86. 86. CHART 76–1 The test results of using a digital meter set to read minimum and maximum values while testing a narrow-band oxygen sensor. * Check for an exhaust leak upstream from the O2S or ignition misfire that can cause a false lean indication before further diagnosis.
    87. 87. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>Good oxygen sensor should sense oxygen content and change voltage outputs rapidly </li></ul></ul><ul><ul><li>How fast oxygen sensor switches from high to low is measured in frequency—number of times voltage switches per second </li></ul></ul>
    88. 88. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>NOTE: On a fuel-injected engine at 2,000 engine RPM, 1 to 5 Hz (one to five switches per second) is normal. </li></ul></ul>
    89. 89. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>Using scan tool, observe oxygen sensor voltages with engine at 2,000 RPM </li></ul></ul>
    90. 90. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>Look for numbers higher than 800 mV and lower than 200 mV </li></ul></ul><ul><ul><li>If frequency is low, oxygen sensor may be contaminated </li></ul></ul>
    91. 91. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If frequency of switching is higher than 5 Hz, look for misfire conditions </li></ul></ul><ul><ul><ul><li>Connect scan tool and start engine. </li></ul></ul></ul>
    92. 92. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If frequency of switching is higher than 5 Hz, look for misfire conditions </li></ul></ul><ul><ul><ul><li>Operate engine at fast idle (2,500 RPM) for two minutes. </li></ul></ul></ul>
    93. 93. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If frequency of switching is higher than 5 Hz, look for misfire conditions </li></ul></ul><ul><ul><ul><li>Observe oxygen sensor activity on scan tool to confirm close-loop operation. </li></ul></ul></ul><ul><ul><ul><ul><li>Select “snapshot” mode </li></ul></ul></ul></ul>
    94. 94. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If frequency of switching is higher than 5 Hz, look for misfire conditions </li></ul></ul><ul><ul><ul><li>Observe oxygen sensor activity on scan tool to confirm close-loop operation. </li></ul></ul></ul><ul><ul><ul><ul><li>Hold engine speed steady and record </li></ul></ul></ul></ul>
    95. 95. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If frequency of switching is higher than 5 Hz, look for misfire conditions </li></ul></ul><ul><ul><ul><li>Play back snapshot and mark each range of oxygen sensor voltage for each frame of snapshot. </li></ul></ul></ul>
    96. 96. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>Good oxygen sensor and PCM should result in most snapshot values at both ends (1 to 300 mV and y00 to 1,000 mV) </li></ul></ul>
    97. 97. Oxygen Sensor Diagnosis <ul><li>Scan Tool Testing </li></ul><ul><ul><li>If most readings are in between, oxygen sensor is not working correctly </li></ul></ul>
    98. 98. Oxygen Sensor Diagnosis <ul><li>Scope Testing </li></ul><ul><ul><li>Scope can be used to test oxygen sensor </li></ul></ul><ul><ul><li>Connect scope to signal wire and ground for sensor </li></ul></ul>
    99. 99. Figure 76-10 Connecting a handheld digital storage oscilloscope to an oxygen sensor signal wire. Check the instructions for the scope as some require the use of a filter to be installed in the test lead to reduce electromagnetic interference that can affect the oxygen sensor waveform.
    100. 100. Oxygen Sensor Diagnosis <ul><li>Scope Testing </li></ul><ul><ul><li>Operate engine in closed loop </li></ul></ul><ul><ul><li>Voltage signal of sensor should be constantly changing </li></ul></ul>
    101. 101. Figure 76-11 The waveform of a good oxygen sensor as displayed on a digital storage oscilloscope (DSO). Note that the maximum reading is above 800 mV and the minimum reading is less than 200 mV.
    102. 102. Oxygen Sensor Diagnosis <ul><li>Scope Testing </li></ul><ul><ul><li>Check for rapid switching from rich to lean and from lean to rich </li></ul></ul><ul><ul><li>Check that change occurs between once every two seconds and five times per second (0.5 to 5.0 Hz) </li></ul></ul>
    103. 103. Oxygen Sensor Diagnosis <ul><li>Scope Testing </li></ul><ul><ul><li>NOTE: General Motors warns not to base the diagnosis of an oxygen sensor problem solely on its scope pattern. The varying voltage output of an oxygen sensor can easily be mistaken for a fault in the sensor itself rather than a fault in the fuel delivery system. </li></ul></ul>
    104. 104. POST CATALYTIC CONVERTER OXYGEN SENSOR TESTING
    105. 105. Post Catalytic Converter Oxygen Sensor Testing <ul><li>Oxygen sensor located behind the catalytic converter is used on OBD-II vehicles to monitor converter efficiency </li></ul>
    106. 106. Post Catalytic Converter Oxygen Sensor Testing <ul><li>Charging air-fuel mixture required for efficient use of converter </li></ul><ul><li>If converter works correctly, oxygen content after converter will be fairly constant </li></ul>
    107. 107. Figure 76-12 The post catalytic converter oxygen sensor should display very little activity if the catalytic converter is efficient.
    108. 108. Post Catalytic Converter Oxygen Sensor Testing <ul><li>Post catalytic converter oxygen sensor also used to modify amount of fuel delivered to engine to increase converter efficiency </li></ul><ul><li>For example, rear oxygen sensor voltage stayed high </li></ul>
    109. 109. Post Catalytic Converter Oxygen Sensor Testing <ul><li>PCM tries to increase amount of oxygen by leaning air-fuel mixture </li></ul><ul><li>Process called target upstream fuel trim </li></ul><ul><li>Instead of PCM commanding target air-fuel mixture of 14.7:1, target may be 14.9:1 to provide extra oxygen for converter </li></ul>
    110. 110. WIDE-BAND OXYGEN SENSORS
    111. 111. Wide-Band Oxygen Sensors <ul><li>Terminology </li></ul><ul><ul><li>Wide-band oxygen sensors used to ensure exhaust emissions meet current standards </li></ul></ul>
    112. 112. Wide-Band Oxygen Sensors <ul><li>Terminology </li></ul><ul><ul><li>Have various names depending on vehicle and sensor manufacturer </li></ul></ul><ul><ul><ul><li>Wide-band oxygen sensor </li></ul></ul></ul><ul><ul><ul><li>Broadband oxygen sensor </li></ul></ul></ul>
    113. 113. Wide-Band Oxygen Sensors <ul><li>Terminology </li></ul><ul><ul><li>Have various names depending on vehicle and sensor manufacturer </li></ul></ul><ul><ul><ul><li>Wide-range oxygen sensor </li></ul></ul></ul><ul><ul><ul><li>Air-fuel ratio (AFR) sensor </li></ul></ul></ul>
    114. 114. Wide-Band Oxygen Sensors <ul><li>Terminology </li></ul><ul><ul><li>Have various names depending on vehicle and sensor manufacturer </li></ul></ul><ul><ul><ul><li>Wide-range air-fuel (WRAF) sensor </li></ul></ul></ul><ul><ul><ul><li>Lean-air fuel (LAF) sensor </li></ul></ul></ul>
    115. 115. Wide-Band Oxygen Sensors <ul><li>Terminology </li></ul><ul><ul><li>Also manufactured in dual cell and single cell designs </li></ul></ul>
    116. 116. Wide-Band Oxygen Sensors <ul><li>Introduction </li></ul><ul><ul><li>Zirconia oxygen sensor reacts to air fuel mixture richer or leaner than 14.7:1 </li></ul></ul><ul><ul><li>Sensor cannot be used to detect an exact air-fuel mixture </li></ul></ul>
    117. 117. Figure 76-13 A conventional zirconia oxygen sensor can only reset to exhaust mixtures that are richer or leaner than 14.7:1 (lambda 1.00).
    118. 118. Wide-Band Oxygen Sensors <ul><li>Introduction </li></ul><ul><ul><li>More stringent exhaust emissions standards require more accurate fuel control </li></ul></ul>
    119. 119. Wide-Band Oxygen Sensors <ul><li>Purpose and Function </li></ul><ul><ul><li>Wide-band oxygen sensor can supply more detailed information to PCM </li></ul></ul><ul><ul><li>Can detect exhaust air-fuel ratio from 10:1 to 23:1 </li></ul></ul><ul><ul><li>Cold start activity within 10 seconds </li></ul></ul>
    120. 120. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>In 1998, Bosch introduced flat, thin wide-band oxygen sensor—planar design </li></ul></ul>
    121. 121. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Thin design allows it to heat quickly and achieve closed loop in 10 seconds </li></ul></ul><ul><ul><li>Fast heating, called light-off time (LOT), improves fuel economy and reduces cold-start emissions </li></ul></ul>
    122. 122. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Conventional oxygen sensor can also be constructed in planar design instead of thimble-type design </li></ul></ul>
    123. 123. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Planar design has these features: </li></ul></ul><ul><ul><ul><li>Elements including zirconia electrolyte, two electrodes, and heater in flat design </li></ul></ul></ul>
    124. 124. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Planar design has these features: </li></ul></ul><ul><ul><ul><li>Faster warm-up because heater is in direct contact with other elements </li></ul></ul></ul>
    125. 125. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Planar design has these features: </li></ul></ul><ul><ul><ul><li>Planar oxygen sensors most commonly used </li></ul></ul></ul>
    126. 126. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Sandwich-type designs of planar style have same elements </li></ul></ul><ul><ul><li>Elements are stacked in the following way from exhaust side to air side: </li></ul></ul><ul><ul><ul><li>Exhaust stream </li></ul></ul></ul>
    127. 127. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Elements are stacked in the following way from exhaust side to air side: </li></ul></ul><ul><ul><ul><li>Outer electrode </li></ul></ul></ul><ul><ul><ul><li>Zirconia (Zr2) (electrolyte) </li></ul></ul></ul>
    128. 128. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Elements are stacked in the following way from exhaust side to air side: </li></ul></ul><ul><ul><ul><li>Inner electrode (reference or signal) </li></ul></ul></ul>
    129. 129. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Elements are stacked in the following way from exhaust side to air side: </li></ul></ul><ul><ul><ul><li>Outside (ambient) air </li></ul></ul></ul><ul><ul><ul><li>Heater </li></ul></ul></ul>
    130. 130. Figure 76-14 A planar design zirconia oxygen sensor places all of the elements together, which allows the sensor to reach operating temperature quickly.
    131. 131. Wide-Band Oxygen Sensors <ul><li>Planar Design </li></ul><ul><ul><li>Another name for conventional oxygen sensor is Nernst cell </li></ul></ul>?
    132. 132. DUAL CELL PLANAR WIDE-BAND SENSOR OPERATION
    133. 133. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Construction </li></ul><ul><ul><li>Dual cell planar-type wide-band oxygen sensor is made like conventional planar O2S </li></ul></ul>
    134. 134. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Construction </li></ul><ul><ul><li>Above the Nernst cell is another Zirconia layer with two electrodes, called the pump cell </li></ul></ul>
    135. 135. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Construction </li></ul><ul><ul><li>The two cells share a common ground, called the reference </li></ul></ul><ul><ul><li>Two internal chambers </li></ul></ul>
    136. 136. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Construction </li></ul><ul><ul><li>The air reference chamber is exposed to ambient air </li></ul></ul><ul><ul><li>Diffusion chamber is exposed to exhaust gases </li></ul></ul>
    137. 137. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Construction </li></ul><ul><ul><li>Platinum electrodes on both sides of Zirconia electrolyte elements </li></ul></ul>
    138. 138. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Operation </li></ul><ul><ul><li>Typical wide-band oxygen sensor has positive or negative voltage signal to balance two sensors </li></ul></ul>
    139. 139. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Operation </li></ul><ul><ul><li>Oxygen sensors do not measure quantity of free oxygen in exhaust </li></ul></ul><ul><ul><li>Sensors produce a voltage based on ion flow between electrodes </li></ul></ul>
    140. 140. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Operation </li></ul><ul><ul><li>PCM can apply a small current to pump cell electrodes causing oxygen ions through zirconia into or out of diffusion chamber </li></ul></ul><ul><ul><li>Process brings voltage back to 0.45 V </li></ul></ul>
    141. 141. Figure 76-15 The reference electrodes are shared by the Nernst cell and the pump cell.
    142. 142. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>When exhaust is stoichiometric (14.7: 1 air-fuel ratio), voltage of Nernst cell is 450 mV (0.45V) </li></ul></ul>
    143. 143. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Voltage between diffusion chamber and air reference chamber changes from 0.45 V </li></ul></ul>
    144. 144. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Voltage will be higher if exhaust is rich </li></ul></ul><ul><ul><li>Voltage will be lower if exhaust is lean </li></ul></ul>
    145. 145. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Reference voltage remains constant </li></ul></ul><ul><ul><li>Typical reference voltages include: </li></ul></ul><ul><ul><ul><li>2.2 V </li></ul></ul></ul><ul><ul><ul><li>2.5 V </li></ul></ul></ul>
    146. 146. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Typical reference voltages include: </li></ul></ul><ul><ul><ul><li>2.7 V </li></ul></ul></ul><ul><ul><ul><li>3.3 V </li></ul></ul></ul><ul><ul><ul><li>3.6 V </li></ul></ul></ul>
    147. 147. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Rich exhaust, voltage between reference electrode and Nerst cell electrode is higher than 0.45 V </li></ul></ul><ul><ul><li>PCM applies negative current to pump cell electrode to balance circuit </li></ul></ul>
    148. 148. Figure 76-16 When the exhaust is rich, the PCM applies a negative current into the pump cell.
    149. 149. Dual Cell Planar Wide-Band Sensor Operation <ul><li>Stoichiometric </li></ul><ul><ul><li>Lean exhaust, voltage between reference electrode and Nerst cell electrode is lower than 0.45 V </li></ul></ul><ul><ul><li>PCM applies positive current to pump cell electrode to balance circuit </li></ul></ul>
    150. 150. Figure 76-17 When the exhaust is lean, the PCM applies a positive current into the pump cell.
    151. 151. DUAL CELL DIAGNOSIS
    152. 152. Dual Cell Diagnosis <ul><li>Scan Tool Diagnosis </li></ul><ul><ul><li>Most service information specifies using scan tool to check wide-band oxygen sensor </li></ul></ul>
    153. 153. Dual Cell Diagnosis <ul><li>Scan Tool Diagnosis </li></ul><ul><ul><li>Even wide-band oxygen sensors can be fooled by exhaust manifold leak or other faults </li></ul></ul>
    154. 154. Dual Cell Diagnosis <ul><li>Scan Tool Diagnosis </li></ul><ul><ul><li>If oxygen sensor reading is false, PCM will command incorrect amount of fuel </li></ul></ul>
    155. 155. Dual Cell Diagnosis <ul><li>Scan Tool Diagnosis </li></ul><ul><ul><li>Scan data on generic OBD-II scan tool will often differ from reading on factory scan tool </li></ul></ul>
    156. 156. CHART 76–2 A comparison showing what a factory scan tool and a generic OBD-II scan tool might display at various air-fuel ratios.
    157. 157. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 1: Check service information and determine the circuit and connector terminal identification. </li></ul></ul></ul>
    158. 158. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 2: Measure the calibration resistor. </li></ul></ul></ul><ul><ul><ul><ul><li>NOTE: The calibration resistor is usually located within the connector itself. </li></ul></ul></ul></ul>
    159. 159. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 2: Measure the calibration resistor. </li></ul></ul></ul><ul><ul><ul><ul><li>If open, ohmmeter will read OL (infinity ohms) </li></ul></ul></ul></ul>
    160. 160. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 2: Measure the calibration resistor. </li></ul></ul></ul><ul><ul><ul><ul><li>If shorted, ohmmeter will read zero or close to zero </li></ul></ul></ul></ul>
    161. 161. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 3: Measure heater circuit for proper resistance or current flow. </li></ul></ul></ul><ul><ul><ul><li>STEP 4: Measure the reference voltage relative to ground. </li></ul></ul></ul><ul><ul><ul><ul><li>Usually 2.4 to 2.6 V </li></ul></ul></ul></ul>
    162. 162. Dual Cell Diagnosis <ul><li>Digital Meter Testing </li></ul><ul><ul><li>Perform the following steps: </li></ul></ul><ul><ul><ul><li>STEP 5: Using jumper wires, connect ammeter and measure the current in the pump cell control wire. </li></ul></ul></ul>
    163. 163. Dual Cell Diagnosis <ul><li>Rich Exhaust </li></ul><ul><ul><li>When the exhaust is rich, Nernst cell voltage moves higher than 0.45 V </li></ul></ul><ul><ul><li>PCM will pump oxygen from exhaust into diffusion gap by applying positive voltage to pump cell </li></ul></ul>
    164. 164. Dual Cell Diagnosis <ul><li>Lean Exhaust </li></ul><ul><ul><li>When exhaust is lean, Nernst cell voltage moves lower than 0.45 V </li></ul></ul><ul><ul><li>PCM will pump oxygen out of the diffusion gap by applying negative voltage to pump cell </li></ul></ul>
    165. 165. Figure 76-18 Testing a dual cell wide-band oxygen sensor can be done using a voltmeter or a scope. The meter reading is attached to the Nernst cell and should read stoichiometric (450 mV) at all times. The scope is showing activity to the pump cell with commands from the PCM to keep the Nernst cell at 14.7:1 air-fuel ratio.
    166. 166. SINGLE CELL WIDE-BAND OXYGEN SENSORS
    167. 167. Single Cell Wide-Band Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Typical single cell wide-band oxygen sensor (air-fuel ratio sensor) has these construction features </li></ul></ul>
    168. 168. Single Cell Wide-Band Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Cap or planar design </li></ul></ul><ul><ul><li>Oxygen pumped into diffusion layer as in operation of dual cell wide-band oxygen sensor </li></ul></ul>
    169. 169. Figure 76-19 A single cell wide-band oxygen sensor has four wires with two for the heater and two for the sensor itself. The voltage applied to the sensor is 0.4 V (3.3 − 2.9 = 0.4) across the two leads of the sensor.
    170. 170. Single Cell Wide-Band Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Current flow reverses positive and negative </li></ul></ul><ul><ul><li>Two cell wires and two heater wires (power and ground) </li></ul></ul>
    171. 171. Single Cell Wide-Band Oxygen Sensors <ul><li>Construction </li></ul><ul><ul><li>Heater usually requires 6 amperes and ground side is pulse-width modulated </li></ul></ul>
    172. 172. Single Cell Wide-Band Oxygen Sensors <ul><li>Milliammeter Testing </li></ul><ul><ul><li>PCM controls single cell wide-band oxygen sensor by maintaining voltage difference of 300 mV (0.3 V) between the two sensor leads </li></ul></ul>
    173. 173. Single Cell Wide-Band Oxygen Sensors <ul><li>Milliammeter Testing </li></ul><ul><ul><li>PCM keeps voltage difference constant by increasing or decreasing current between the elements of the cell </li></ul></ul><ul><ul><ul><li>Zero (0mA) represents lambda, or stoichiometric air-fuel ratio of 14.7:1 </li></ul></ul></ul>
    174. 174. Single Cell Wide-Band Oxygen Sensors <ul><li>Milliammeter Testing </li></ul><ul><ul><li>PCM keeps voltage difference constant by increasing or decreasing current between the elements of the cell </li></ul></ul><ul><ul><ul><li>+ 10 mA indicates lean condition </li></ul></ul></ul>
    175. 175. Single Cell Wide-Band Oxygen Sensors <ul><li>Milliammeter Testing </li></ul><ul><ul><li>PCM keeps voltage difference constant by increasing or decreasing current between the elements of the cell </li></ul></ul><ul><ul><ul><li>– 10 mA indicates rich condition </li></ul></ul></ul>
    176. 176. Single Cell Wide-Band Oxygen Sensors <ul><li>Scan Tool Testing </li></ul><ul><ul><li>Scan tool will display voltage reading but it can vary </li></ul></ul><ul><ul><li>Depends on type and maker of tool </li></ul></ul>
    177. 177. WIDE-BAND OXYGEN PATTERN FAILURES
    178. 178. Wide-Band Oxygen Pattern Failures <ul><li>Wide-band oxygen sensors have long life, but can fail </li></ul><ul><li>Most failures will cause diagnostic trouble code (DTC) to set </li></ul><ul><li>Usually malfunction indicator (check engine) lamp will light </li></ul>
    179. 179. Wide-Band Oxygen Pattern Failures <ul><li>One failure may not set up DTC </li></ul><ul><ul><li>Voltage from heater circuit bleeds into Nernst cell </li></ul></ul><ul><ul><li>Voltage will cause engine to operate extremely lean </li></ul></ul><ul><ul><li>May or may not set a diagnostic trouble code </li></ul></ul>
    180. 180. OXYGEN SENSOR– RELATED DIAGNOSTIC TROUBLE CODES
    181. 181. Oxygen Sensor-Related Diagnostic Trouble Codes
    182. 182. FREQUENTLY ASKED QUESTION <ul><li>What Happens to the Bias Voltage? </li></ul><ul><ul><li>Some vehicle manufacturers such as General Motors Corporation have the PCM apply 450 mV (0.45 V) to the O2S signal wire. This voltage is called the bias voltage and represents the threshold voltage for the transition from rich to lean. </li></ul></ul>? BACK TO PRESENTATION <ul><li>This bias voltage is displayed on a scan tool when the ignition switch is turned on with the engine off. When the engine is started, the O2S becomes warm enough to produce a usable voltage, and bias voltage “disappears” as the O2S responds to a rich and lean mixture. What happens to the bias voltage that the PCM applies to the O2S? The voltage from the O2S simply overcomes the very weak voltage signal from the PCM. </li></ul><ul><li>This bias voltage is so weak that even a 20 megohm impedance DMM will affect the strength enough to cause the voltage to drop to 426 mV. Other meters with only 10 megohms of impedance will cause the bias voltage to read less than 400 mV. </li></ul><ul><li>Therefore, even though the O2S voltage is relatively low powered, it is more than strong enough to override the very weak bias voltage the PCM sends to the O2S. </li></ul>
    183. 183. REAL WORLD FIX <ul><li>The Chevrolet Pickup Truck Story </li></ul><ul><ul><li>The owner of a 1996 Chevrolet pickup truck complained that the engine ran terribly. It would hesitate and surge, yet there were no diagnostic trouble codes (DTCs). After hours of troubleshooting, the technician discovered while talking to the owner that the problem started after the transmission had been repaired. </li></ul></ul><ul><li>However, the transmission shop said that the problem was an engine problem and not related to the transmission. </li></ul><ul><li>A thorough visual inspection revealed that the front and rear oxygen sensor connectors had been switched. The PCM was trying to compensate for an air-fuel mixture condition that did not exist. Reversing the O2S connectors restored proper operation of the truck. </li></ul>BACK TO PRESENTATION
    184. 184. FREQUENTLY ASKED QUESTION <ul><li>Where Is HO2S1? </li></ul><ul><ul><li>Oxygen sensors are numbered according to their location in the engine. On a V-type engine, heated oxygen sensor number 1 (HO2S1) is located in the exhaust manifold on the side of the engine where cylinder 1 is located. </li></ul></ul>? BACK TO PRESENTATION <ul><ul><li>Figure 76-6 Number and label designations for oxygen sensors. Bank 1 is the bank where cylinder 1 is located. </li></ul></ul>
    185. 185. REAL WORLD FIX <ul><li>The Oxygen Sensor Is Lying to You </li></ul><ul><ul><li>A technician was trying to solve a driveability problem with an older V-6 passenger car. The car idled roughly, hesitated, and accelerated poorly. A thorough visual inspection did not indicate problems and there were no diagnostic trouble codes stored. </li></ul></ul><ul><li>The technician checked the oxygen sensor activity using a DMM. The voltage stayed above 600 mV most of the time. If the technician removed a large vacuum hose, the oxygen sensor voltage would temporarily drop to below 450 mV and then return to a reading of over 600 mV. Remember: </li></ul>BACK TO PRESENTATION <ul><ul><li>High O2S readings = rich exhaust (low O 2 content in the exhaust) </li></ul></ul><ul><ul><li>Low O2S readings = lean exhaust (high O 2 content in the exhaust) </li></ul></ul><ul><li>As part of a thorough visual inspection, the technician removed and inspected the spark plugs. All the spark plugs were white, indicating a lean mixture, not the rich mixture that the oxygen sensor was indicating. The high O2S reading signaled the PCM to reduce the amount of fuel, resulting in an excessively lean operation. </li></ul><ul><li>After replacing the oxygen sensor, the engine ran great. But what killed the oxygen sensor? The technician finally learned from the owner that the head gasket had been replaced over a year ago. The silicate and phosphate additives in the antifreeze coolant had coated the oxygen sensor. Because the oxygen sensor was coated, the oxygen content of the exhaust could not be detected, resulting in a false rich signal from the oxygen sensor. </li></ul>
    186. 186. REAL WORLD FIX <ul><li>The Missing Ford </li></ul><ul><ul><li>A Ford was being analyzed for poor engine operation. The engine ran perfectly during the following conditions. </li></ul></ul><ul><ul><ul><li>Engine cold or operating in open loop </li></ul></ul></ul><ul><ul><ul><li>Engine at idle </li></ul></ul></ul><ul><ul><ul><li>Engine operating at or near wide-open throttle </li></ul></ul></ul><ul><li>After hours of troubleshooting, the technician determined the cause to be a poor ground connection for the oxygen sensor. The engine ran okay during times when the PCM ignored the oxygen sensor. Unfortunately, the service technician did not have a definite plan during the diagnostic process and as a result checked and replaced many unnecessary parts. </li></ul>BACK TO PRESENTATION <ul><li>An oxygen sensor test early in the diagnostic procedure would have indicated that the oxygen (O2S) signal was not correct. The poor ground caused the oxygen sensor voltage level to be too high, indicating to the PCM that the mixture was too rich. The PCM then subtracted fuel which caused the engine to miss and run roughly as the result of the now too lean air-fuel mixture. </li></ul>
    187. 187. TECH TIP <ul><li>Do Not Solder Oxygen Sensor Wires </li></ul><ul><ul><li>Oxygen sensors must have outside oxygen to compare with the oxygen content in the exhaust. Most oxygen sensors breathe through the signal wire and, if soldered, would block the flow of outside air to the sensor. </li></ul></ul>BACK TO PRESENTATION <ul><li>If a replacement oxygen sensor is used, always use the factory replacement, using the original connectors or a crimp-and-seal connector that will seal out any moisture and still allow air to flow through the connector. </li></ul>
    188. 188. FREQUENTLY ASKED QUESTION <ul><li>Why Does the Oxygen Sensor Voltage Read 5 Volts on Many Chrysler Vehicles? </li></ul><ul><ul><li>Many Chrysler vehicles apply a 5 volt reference to the signal wire of the oxygen sensor. The purpose of this voltage is to allow the PCM to detect if the oxygen sensor signal circuit is open or grounded. </li></ul></ul>? <ul><ul><li>If the voltage on the signal wire is 4.5 volts or more, the PCM assumes that the sensor is open. </li></ul></ul><ul><ul><li>If the voltage on the signal wire is zero, the PCM assumes that the sensor is shorted-to-ground. </li></ul></ul><ul><li>If either condition exists, the PCM can set a diagnostic trouble code (DTC). </li></ul>BACK TO PRESENTATION
    189. 189. TECH TIP <ul><li>The Key On, Engine Off Oxygen Sensor Test </li></ul><ul><ul><li>This test works on General Motors vehicles and may work on others if the PCM applies a bias voltage to the oxygen sensors. Zirconia oxygen sensors become more electrically conductive as they get hot. To perform this test, be sure that the vehicle has not run for several hours. </li></ul></ul><ul><li>STEP 1 Connect a scan tool and get the display ready to show oxygen sensor data. </li></ul><ul><li>STEP 2 Key the engine on without starting the engine. The heater in the oxygen sensor will start heating the sensor. </li></ul>BACK TO PRESENTATION <ul><li>STEP 3 Observe the voltage of the oxygen sensor. The applied bias voltage of 450 mV should slowly decrease for all oxygen sensors as they become more electrically conductive as the bias voltage is flowing to ground. </li></ul><ul><li>STEP 4 A good oxygen sensor should indicate a voltage of less than 100 mV after three minutes. Any sensor that displays a higher than usual voltage or seems to stay higher longer than the others could be defective or skewed high. </li></ul>
    190. 190. TECH TIP <ul><li>The Propane Oxygen Sensor Test </li></ul><ul><ul><li>Adding propane to the air inlet of a running engine is an excellent way to check if the oxygen sensor is able to react to changes in air-fuel mixture. Follow these steps in performing the propane trick. </li></ul></ul>BACK TO PRESENTATION <ul><li>Connect a digital storage oscilloscope to the oxygen sensor signal wire. </li></ul><ul><li>Start and operate the engine until it reaches operating temperature and is in closed-loop fuel control. </li></ul><ul><li>While watching the scope display, add some propane to the air inlet. The scope display should read full rich (over 800 mV). </li></ul><ul><li>Shut off the propane. The waveform should drop to less than 200 mV (0.2 V). </li></ul><ul><li>Quickly add some propane while the oxygen sensor is reading low and watch for a rapid transition to rich. The transition should occur in less than 100 milliseconds (ms). </li></ul>
    191. 191. REAL WORLD FIX <ul><li>How Could Using Silicone Sealer on a Valve Cover Gasket Affect the Oxygen Sensor? </li></ul><ul><ul><li>The wrong type of silicone room temperature vulcanization (RTV) sealer on a valve cover gasket gives off harmful silica fumes during the curing process. </li></ul></ul><ul><li>These fumes enter the crankcase area by way of the oil drainback holes in the cylinder head as well as through pushrod openings and other passages in the engine. During engine operation, these fumes are drawn into the intake manifold through the positive crankcase ventilation (PCV) system and are burned in the engine. </li></ul>BACK TO PRESENTATION <ul><li>The harmful silica then exits through the exhaust system, where the contamination affects the oxygen sensor. </li></ul><ul><li>NOTE: Be careful not to spray any silicone lubricant near the engine vacuum, which might draw the fumes into the engine and cause silica damage to the oxygen sensor. </li></ul>
    192. 192. FREQUENTLY ASKED QUESTION <ul><li>How Quickly Can a Wide-Band Oxygen Sensor Achieve Closed Loop? </li></ul><ul><ul><li>In a Toyota Highlander hybrid electric vehicle, the operation of the gasoline engine is delayed for a short time when the vehicle is first driven. During this time of electric operation, the oxygen sensor heaters are turned on in readiness for the gasoline engine starting. </li></ul></ul>? BACK TO PRESENTATION <ul><li>The gasoline engine often achieves closed-loop operation during cranking because the oxygen sensors are fully warm and ready to go at the same time the engine is started. Having the gasoline engine achieve closed loop quickly, allows it to meet the stringent SULEV standards. </li></ul>

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