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Old 02-12-2007, 11:23 AM   #1
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Default Trac Control/Stability system kicks in intermittently

Low Trac light comes on, left front brake is modulated by the stab system trying to correct a non-existent problem. Pulls the left front wheel. Had "service stab system" message, and dlr replaced control module (EBCM?). No more warning, but problem didn't go away. Replaced both front wheel speed sensors (hubs w/ bearings) - didn't solve problem. Wheel balance, alignment, rotors all ok. NO codes are generated. I also get a random retard once in a while for a second or two like the engine or transaxle is being overridden. Any ideas? Any way to diagnose? $1770 sunk chasing this problem so far.
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Old 02-12-2007, 11:25 AM   #2
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Default Re: Trac Control/Stability system kicks in intermittently

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Originally Posted by EdMc
Low Trac light comes on, left front brake is modulated by the stab system trying to correct a non-existent problem. Pulls the left front wheel. Had "service stab system" message, and dlr replaced control module (EBCM?). No more warning, but problem didn't go away. Replaced both front wheel speed sensors (hubs w/ bearings) - didn't solve problem. Wheel balance, alignment, rotors all ok. NO codes are generated. I also get a random retard once in a while for a second or two like the engine or transaxle is being overridden. Any ideas? Any way to diagnose? $1770 sunk chasing this problem so far.
Can you put your car description for miles and age in your profile so it'* posted when you pos?

My guess would be a sensor rather than the control module. What did the TechII say for any errors store in the system?
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Old 02-12-2007, 12:57 PM   #3
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Having it scanned when it happens may be the only way to track down the problem. If there is a stored code for it, even better. There are various parts that could cause the problem, and some are not particularly cheap, so guessing isn't really an option.

The rear wheel speed sensors could also cause the problem, as well as the steering position sensor, yaw sensor, or lateral accelerometer.
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Old 02-12-2007, 03:29 PM   #4
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Thanks for the replies. The problem has thrown no codes, which makes it a real puzzle. I probably will try to catch what'* going on real time with a tech using a breakout box to monitor.
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Old 02-12-2007, 04:13 PM   #5
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It does sound as if some real time analysis is going to be the way to track it down. You may want to start with checking the pulses from the rear hubs. If I hit a bump just right with the right rear, it would set of my stability system warning on the DIC. Since replacing that hub, I haven't had any further problems. Gives you at least a starting point.
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Old 02-12-2007, 06:07 PM   #6
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My thinking it might be a sensor such as the "yaw" sensor under the rear shelf if because I had parked uphill and sloped left or right at a garden center. Leaving their parking lot making a right turn as I speeded up to 15 or so the left front started grinding with a brake application that pulsed. I pulled over and restarted the car a few hundred feet up the road. No more problem.

I suspect the sensor moving part inside the yaw sensor somehow was fooled, stuck, whatever.

Has anyone taken one of those apart?
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Old 02-12-2007, 07:38 PM   #7
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LOW TRAC & left front brake modulating? That seems to point to the problem, maybe. The EBCM thinks that left front wheel is slipping when in fact it isn't. I'd take a closer look at the wss connector on the left front wheel. Check continuity from the wss connector end to the EBCM C2 connector. Pin A at wss should terminate at pin 11 at EBCM, pin B at wss should terminate at pin 25 at EBCM. Wiggle the wss connector while reading out those leads for intermittent continuity. The other thing I was thinking, this is a shot in the dark, disconnect the steering wheel position sensor connector. It will more than likely generate a DTC, but just take the DTC for now, clear it later. Then see if that problem with left front braking reappears, or disappears. Just a few ideas.
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Old 02-12-2007, 07:59 PM   #8
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Why is this not simply the Steering Position Sensor that has a high failure rate? Mine with 25K miles did nearly all the same things. Trac light, brake kicking in, cruise dissengauging, and a random Service Stability System message. From what I can tell, it'* the first place to start on these kind of issues. Patrick
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Old 02-12-2007, 10:16 PM   #9
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Quote:
Originally Posted by markwb
The other thing I was thinking, this is a shot in the dark, disconnect the steering wheel position sensor connector. It will more than likely generate a DTC, but just take the DTC for now, clear it later. Then see if that problem with left front braking reappears, or disappears. Just a few ideas.
I had to re-think this, maybe not a good idea after all. Disconnecting the steering wheel position sensor electrically will disable the Stabilitrac completely which wouldn't really prove anything. Real time analysis like Archon mentioned is probably your best bet. I think Tech II scan tool will do this. Someone correct me if I'm wrong.
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Old 02-12-2007, 10:34 PM   #10
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I agree Mark. I was thinking of him disabling different hubs and sensors too, but then thought that would disable the entire system.

Ivory, it is possible that the steering position sensor is the problem. Some diagnostic procedures to track the problem is preferable over throwing parts at the problem. In particular one that is not real easy to replace.
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