2001 4.0l Aurora - ABS and Trac Off light constantly on - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-10-2014, 08:53 PM   #1
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Default 2001 4.0l Aurora - ABS and Trac Off light constantly on

This is a rather long post, but it has lots of info because I have been troubleshooting for a while and am just lost now.

I have a 2001 4.0l Aurora with 193k miles, I bought it with 118k 7 years ago. For the past two months, the ABS and Trac Off light would sporadically turn on and off with no discernible pattern. About a week ago the ABS and Trac Off light came on, and have stayed on every time I have turned the car on. At the same time, I noticed that the brake pedal was not as stiff as usual. It would behave like what I thought to be normal until about half way down, and then with constant pressure, it would just mush down the rest of the way. Thinking there was a leak, I checked all of the lines and was unable to find a leak. I then bled the lines and did not get any air bubbles. Additionally, there was no fluid loss occurring from the reserve. Given that the brake master cylinder appeared to be the original, I replaced the master cylinder. I bench bled the master cylinder, and rebled the brake lines. Again, no bubbles and no fluid loss. I expected this to fix the problem but it did not. I still have mushy brakes, and I still have an ABS and Trac Off light on constantly. The thing is, it doesn't drive like there is a loss of fluid. Additionally, I haven't had to put any fluid in since I replaced the master cylinder. I can drive it around on the streets and it behaves almost like normal. If I try to go above 40 and hit the brakes hard, that'* where the performance difference appears. At that point, its very obvious that the brakes aren't performing up to expectations, and my foot is at the floor before the car stops properly.

Not sure what to do, I purchased the Palmer Performance ScanXL Standard, and GM Enhanced diagnostics software/hardware to pull the advanced OBD codes. Below is the list of codes that popped.

P1571 Traction Control Torque Request Circuit
U1040 Lost Communications with Brake/Traction Control System
C1221 Left Front Wheel Speed Sensor Input Signal = 0
C1222 Right Front Wheel Speed Sensor Input Signal = 0
C1223 Left Rear Wheel Speed Sensor Input Signal = 0
C1224 Right Rear Wheel Speed Sensor Input Signal = 0
C1234 Left Rear Wheel Speed Sensor Circuit Open or Shorted
C1235 Right Rear Wheel Speed Sensor Circuit Open or Shorted
C1238 Brake Thermal Model Exceeded
C1241 Variable Effort Steering Circuit Malfunction
C1242 Pump Motor Circuit Open
C1243 Pump Motor Stalled
C1248 DRP Disabled
C1254 Abnormal Shutdown Detected
C1277 Requested Torque Signal Circuit Malfunction
C1282 Yaw Rate Sensor Bias Circuit Malfunction
C1283 Excessive Time to Center Steering
C1287 Steering Sensor Rate Malfunction
C1288 Steering Sensor Circuit Malfunction
C1295 Brake Lamp Switch Circuit Open
C1298 PCM Class 2 Serial Data Link Malfunction
U1255 Loss of Class 2 Communication

Now granted, it could have had some of these codes before and I just wasn't able to read them with the basic OBD reader I had, but that'* a lot of codes!

Given the number of codes, I don't know where to even begin. What am I missing here? Any recommended next steps? I'm about ready to light the aurora on fire and dance naked around my offering to the car gods.
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Old 02-10-2014, 09:06 PM   #2
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These 2...
C1298 PCM Class 2 Serial Data Link Malfunction
U1255 Loss of Class 2 Communication

All modules in the car talk to each other via the data bus. Gotta figure out why its not talking to the ABS system.
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Old 02-10-2014, 09:29 PM   #3
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If the EBCM went bad would it throw those codes? Or should I be checking for faulty wiring/connectors?
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Old 02-10-2014, 10:20 PM   #4
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I'd start with grounds from the EBCM working backwards.
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Old 02-11-2014, 07:51 AM   #5
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im guessing loss of ebcm would cause all the rest. so like mike said check for power and ground to it first then it might be something in it
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Old 02-12-2014, 02:52 AM   #6
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Progress has been made! But I'm still having problems...

Short Version:
I only have 4 ABS codes now.
C1242 Pump Motor Circuit Open
C1243 Pump Motor Stalled
C1287 Steering Sensor Rate Malfunction
C1288 Steering Sensor Circuit Malfunction

Long Version:
I cleared the DTC codes before beginning to work on it today.
I disconnected the two EBCM connectors, as well as the main wiring harness connector, sprayed them down with electronics cleaner and reconnected them.
I disconnected the Wheel Speed Sensors, sprayed them with electronics cleaner and reconnected them.
I checked the wires from the WSS to the EBCM, and the EBCM connector to the main harness and was unable to find any damage/breaks. All of the wiring still had the protective sheathing on it, and did not seem to have any damage.

The only wiring that was out of place were two wires that the previous owner had added to the harness. They cut a white and a brown wire from the main wiring harness connector, and ran two wires to the the EBCM connector where they connected them to a white and brown wire again. They have been like that since I first got the car 7 years ago, and I checked the soldered connections so I don't believe that is the problem.

I am somewhat concerned because I was not able to find a ground strap. I thought that this module had a ground strap that connects the EBCM to the frame, but I didn't find it. So either, I didn't look hard enough, or it doesn't have one. I found the big main connection that is on the side of the EBCM, and the smaller connection with two wires that goes underneath the EBCM.

It seems like the two possibilities are: 1) I missed the ground strap and its messing with the EBCM 2)the BPMV went bad and I need a new one.

Any thoughts/suggestions?
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