1. Auto 131 Lab Experience Report
Part 1: Vehicle Information
Student name(s):
TJ Mathews
Eddy Torres
Vehicle year, make, model:
1994 Jeep Cherokee
Customer’s name & repair order number:
Austin Laibly 9897
Customer’s concern(s):
Driver side window door is not working, but the switch moves the rest of the windows. Radio
doesnt turn on.
Part 2: Documentation
Document the steps you took to diagnose and repair the vehicle—in the order that you did
them. Write every step—even if you made mistakes and now wish you would have done it
differently. Begin when you picked up the keys, end when you returned them. BE
DETAILED & INCLUDE PHOTOGRAPHS!
After we picked up the keys from the office
It took us awhile to find the vehicle
because the secretary was not very
specific on where the car was parked. All
she said was that it was parked
somewhere on center street and didn't
give us the color or licence plate. We
found a total of 4 vehicles of the same
make and year parked in different spots
on center street. Two of them had the
service tag from the automotive department and our key unlocked both cars. Luckily we
were able to locate the right one and our keys only started the engine of one of the cars. As
soon as we found the right vehicle, we verified that the driver side window and the radio
were not working. Then we brought the car In the shop, opened the hood, and performed a
visual inspection. Since everything seemed to be normal in the inspection, we searched for
possible Technical Service Bulletins but nothing relevant to our repair was found. We
decided to look and study the wiring diagram for the driver side circuit and started narrowing

2. down the problem by isolating each
component and verifying that they
were working properly. We started
by measuring the state of charge of
the battery with our multimeter and
measured 12.5 V. Since we had
good voltage in the battery, we could
move on to the next component in
the circuit and continue narrowing
down the problem. We went back to
the wiring diagram and found out
that there’s only two cables that connect the window motor to the switch. These cables can
switch between power and ground depending on whether the switch is pressed for the
window to go up or down. Knowing this, we decided to use a test light to see if all the
components were getting power and ground to energize the circuit.
We managed to locate where the switch was and began to remove the door panel. Once all
the cables were visible, we reconnected the master switch to start the testing. Since the
battery was closer to the passenger side of the car, we had to use jumper cables connected
to each other to reach the driver’s door. The
wiring diagram showed that there was a light
blue and a white cable that connected power
and ground from the switch to the motor. We
decided to start there since it was easy to
access and it was right in the outer terminals of
the switch. After we back probed the terminal,
when we pressed the switch to go up the test
light turned on. Then we connected the jumper
cables to the ground side of the circuit and ran
the same test but this time when pressing the
window down, the test light turned on, proving
that we had power and ground coming from the
battery to the window switch. These results
were very exciting because it meant that until
that point of the circuit we had continuity, good
power and good ground. So every component going to the battery including the switch had

3. current flowing. The only components left were the
window motor, and the two cables connected to it.
To keep narrowing down the problem, we back
probed the cables all the way to the window motor
and found that the test light turned on when the
window was going up and down, meaning that our
power and ground to that point was good. We had
narrowed the problem down to the point where we
knew that the only component that was not working
was the window motor. We decided to do a voltage
drop in the window motor just to make sure we
were getting enough voltage to move the motor.
Our measurement was 12.15 V. Since the voltage
drop showed that there was good voltage going
into the motor, but the motor was not moving, a continuity test was performed in the motor
with the multimeter in the ohm setting. We turned on the beeping mode, and as soon as we
connected it to the motor it started beeping, confirming that there was continuity in the
component.
Once we were confident that we found the root of the
problem, we went to omnique to search for a
compatible part, and after getting approval from the
customer the part was ordered. Once the part arrived,
we found that the part we received from NAPA did not
have the right gears on the motor. We looked to see if
the other motors listed had the right gears but we
decided that we could just take the lock ring off of the
old motor and remove the gears and then switch the
gears with the new motor. We were not very sure if it
would actually work but to our amazement it was a
perfect fit.
We went ahead and moved to the next complaint which was the radio not working. A printed
a wiring diagram was located, and we studied it for a moment. Then we decided to take the
radio apart and back probe each one of the components to narrow down the search just like
we did to the window motor. This time, instead of using the testlight, we decided to use the

4. voltmeter because we not only wanted to know if we had
power going through the system, but we wanted to know
exactly how much voltage we were getting in each
cable. We tested the power and ground coming from the
battery to the radio module and measured 12.5 V. then
with the keys in the run position and we connected our
leads to the ground and to the power cables of the
ignition switch and found no voltage, meaning that there
was an open circuit somewhere. We followed the
ignition cable to the actual fuse box and found that the
15 amps fuse for the radio ignition was blown, which is
why we thought about using a breaker switch instead of
putting a new one, to try to find why it blew in the first
place. After speaking with Brother Schmalle, we went
ahead and connected our leads to the positive side of the battery and with our test light
touched the positive side of the terminal where the fuse was connected and negative side of
the circuit where the fuse was blown and our test light turned on, letting us know that there
was no short to ground in the positive side. Afterwards we decided to connect a fuse breaker
to try to double check if the fuse would blow, but the radio worked just fine. We tried using it
with the car turned on, tried increasing the volume,
moving the wires, and nothing tripped the circuit
breaker, confirming us that there was no short circuit.
Then we went ahead and went to the tool room and
billed a new 15 amp fuse for that vehicle and
proceeded to install it. The repair was verified, and the
fuse was never blown again. We went ahead and
installed everything back together, but we couldn't find
one of the clips for the door handle to open the door.
we didn’t think that it would matter much, because that
clip was just holding the rod to open or close the door,
so we decided to go put it back in together without it,
but when we tried to use the handle, it wouldn't lock or
open the door. We had to go back and disassemble the
door again, find the missing door clip, install it correctly and reassemble the door back again.
Before calling the customer, we verified both the complaints, showed it to our instructor,

5. cleared all the errors in omnique, printed off the repair order onto pink paper for the office
and Brother Schmalle. We finished by parking the car on center street as well as turning the
keys and the paper into the automotive office. After this we called the customer and told
them their car was ready for pickup.
​Part 3: Reflection & Analysis
∙​ ​What parts of this process went well?
The parts of the process that went well we thought were we followed the diagnostic
procedures. We also felt like we were able to focus on one of the problems before we moved
onto the next problem.
∙​ ​Which steps were most critical in your diagnosis process?
Studying the wiring diagram and knowing how the circuit works before we performed all the
tests was one of the most important steps to diagnose this vehicle. Because we decided to
spend a little bit more time understanding the wiring diagrams, it was easier for us to
determine which test to perform to find the problem.
∙​ ​What kept you from being as effective as you could have been?
We should’ve started by testing the component that had the problem. If we would’ve started
by doing voltage drop to the window motor, we would’ve been able to diagnose the problem
a lot faster.
∙​ ​Now that you can look back on how this project unfolded, what would you like to do
differently next time?
Everything went fairly smoothly. It would’ve been useful to know more details about the
vehicle and we wouldn't have wasted so much time finding the vehicle. Other than that, we
were able to methodically follow the diagnosis process to find the problem in a timely
manner.