A wheel speed sensor or vehicle speed sensor (VSS) is a type of tachometer. It is a sender device used for reading the speed of a vehicle's wheel rotation.

1. How Does An Engine Speed Sensor Work?
Sensor
- Speed
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By Liam - http://speedsensor.org/
Engine speed sensors, which are not to be confused with a vehicle speed sensor, are sensors that are
attached to the crankshaft of a car's engine. The purpose of an engine speed sensor is to assess the
speed at which the crankshaft spins. These speed sensors are electronic control devices which are used
in automotive internal combustion engines. This component sends crucial information to the engine
control module (ECM). Crankshaft sensors are used to measure the speed of the crankshaft rotation.
The information from a crankshaft speed sensor is used to control the engine management and ignition
timing systems. These devices first appeared on engines when distributors were eliminated in the early
1990s. The crankshaft sensor serves the same purpose as the ignition pick up and trigger wheel, which is
to adjust the spark timing of the spark plugs. The ignition coil is connected directly to the spark plugs.
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How the Engine Sensor Works
The device is basically a metal disk that has a serrated (toothed) circumference. In addition, there's a
stationary device containing a magnetic coil, which acts as a standard for the measurement. When the

2. crankshaft spins, induction current is set up around the magnetic coil. The serrated edge of the
crankshaft obstructs the produced magnetic field and this is recorded. This is what gives a measurement
of the amount of current produced, which is outputted as the speed of the vehicle's engine.
Basic timing information is sent from the crankshaft sensor to the ECM. The engine RPM (revolutions per
minute), timing and firing order are determined by the information which is received from the
crankshaft timing sensor. The information tells the ECM how fast the engine is running so the ignition
can be advanced or retarded accordingly.
The magnetic type of crankshaft speed sensor uses a magnet to generate an alternating current signal
and sends this to the ecu. The magnet senses the notches in the crankshaft, and the sensation changes
the magnetic field. The frequency of the pulses is calculated by the computer as rotations of the
crankshaft. The Hall Effect type of crankshaft sensor uses blades, which are fixed on the crankshaft. The
blades disrupt the magnetic field in the Hall Effect window. This allows the sensor to switch on and off
and alternate the current. This produces a signal which the ECM reads to determine the crankshaft
speed and position.
So… What’s Next ?
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