2002 GT ABS and Traction Off Lights

[mikeswaggs]

Originally Posted by bnaylor

The problem is GM dealers are about the only ones that can properly scan a GM ABS braking system. They use a Tech 1 or 2 machine. The GP service manual recommends clearing all DTC error codes and confirming the error again before replacing any parts.

The proper name for the ABS control module is EBCM/EBTCM. Electronic Brake Control Module/Electronic Brake & Traction. Its located on the driver's side of the dashboard. Left of the instrument panel. Dash trim and panels have to be removed to get to it.

I'm not 100% sure but the GM part number should be 16268781. GM List $737. GMPARTSDIRECT.COM $420. If its confirmed bad, I'd try to get one at a salvage yard. BTW - The GTP model has its own specific control module. You cannot use one off of a GT or SE Grand Prix. The part numbers are different. Any way you look at it, its expensive and you might consider getting a second opinion from another dealer or shop that has ABS scan capability. Good luck!

I have this same problem with my 2002 Grand Prix GT. It seems that most people with ABS/TRAC OFF light issues has the lights coming on when they begin driving. My lights come on when the car is started and NEVER turn off. About a year ago, the lights would turn on and off, but after a while, since I didn't do anything about it, they just stayed on all the time. Any thoughts? Is there any way to perhaps 'reboot' the ebcm/ebtcm? Perhaps unplug the module? Has anyone had this same problem, lights on ALL the time, and found it was just a wheel speed sensor?

Thanks!

mikeswaggs
2002 Grand Prix GT

[BNaylor]

Originally Posted by mikeswaggs

I have this same problem with my 2002 Grand Prix GT. It seems that most people with ABS/TRAC OFF light issues has the lights coming on when they begin driving. My lights come on when the car is started and NEVER turn off. About a year ago, the lights would turn on and off, but after a while, since I didn't do anything about it, they just stayed on all the time. Any thoughts? Is there any way to perhaps 'reboot' the ebcm/ebtcm? Perhaps unplug the module? Has anyone had this same problem, lights on ALL the time, and found it was just a wheel speed sensor?

Thanks!

mikeswaggs
2002 Grand Prix GT

I moved your post to a new thread. The old one you replied in was was too old and we prefer that threads over 3 months old are not resurrected.

On the EBTCM module there is really no reboot per se but you can try pulling the ABS fuse and see what it does. It sounds like the module is failing self test and most likely not a wheel sensor. Or maybe it is just a lamp driver problem related to the module. At ignition to on not start what do the ABS and TRAC lights do?

[obd2scannerman]

You don't need a Tech2 scanner. A snapon would work if it was updated. A wheel speed sensor if shorted or open will set the light as soon as the vehicle is started. Most likely repair will be a sensor. It could very well be unpluged also, or have damaged wiring near the wheel.

[mikeswaggs]

I have updates. I went to a friends shop and scanned the system. The code came up c0035(if memory serves) left front speed sensor circuit malfunction. We were able to drive the car with the scanner connected and read wheel speeds at all four wheels. The left front sensor was frozen, and the other wheels registered speed. First we cleaned the connector at the sensor and checked the resistance. The reading was 1.029 Kohms. We could not clear the code, or cause the lights to go out. Also, the sensor still did not register any speed. At this time, our thoughts are to test the continuity of the wires from the wheel to the EBCM/EBTCM, if they travel directly there. One further test we did was to plug in a new hub/sensor into the system without installing it to see if a new sensor would complete the circuit and let us clear the codes. It did not. So my thought is to check for continuity, and if it is ok, then replace the hub. Does anyone know why the codes may not clear? Does the system need to read speed at the wheel before it would clear? Perhaps the hub needs to be installed so the hub can ground on the car for the sensor to complete the circuit? Any thoughts would be great. Also, I was looking at a Timken bearing. Does this one satisfy the 'don't buy the white box china garbage' suggestion? Thanks!!!

[BNaylor]

The resistance reading you are getting on the wheel sensor is in the ballpark and acceptable. The DTC you are getting indicates a sensor circuit malfunction related to somewheres in the complete circuit consisting of wheel sensor, wiring and the EBTCM module. In my experiences if it was just an open or shorted wheel sensor the DTCs would be different. C1221 and up to C1235 rings a bell. Before replacing the hub have you checked wheel sensor output with a voltmeter directly at the connector while spinning the wheel?

The way ABS diagnostics works is it will run initialization at startup and once the car reaches a certain speed because it needs to look at wheel sensor input. If all is OK then the faults should not be present. It performs an automatic reset.

The EBCM performs 1 initialization test each ignition cycle. The initialization of the EBCM occurs when 1 set of the following conditions occur:
Both of the following conditions occur:

* The EBCM detects that there is a minimum of 500 RPM from the PCM via a serial data message.
* The stop lamp switch is not applied.

OR
Both of the following conditions occur:

* The vehicle speed is greater than 16 km/h (10 mph).
* The stop lamp switch is applied.

The initialization sequence may also be commanded with a scan tool.

The initialization sequence cycles each solenoid valve and the pump motor, as well as the necessary relays, for approximately 1.5 seconds to check component operation. The EBCM sets a DTC if any error is detected. The initialization sequence may be heard and felt while it is taking place, and is considered part of normal system operation.

The EBCM defines a drive cycle as the completion of the initialization sequence.

[mikeswaggs]

So then, if I check for continuity, and it is fine between the sensor and the EBCM, and I check the sensor with a voltmeter and spinning the wheel, and I have output, would we assume that the EBCM is bad?

[BNaylor]

I would not make any assumption but your course of action looks fine to me. It is better to properly troubleshoot and determine which direction to head. No need wasting money or time on parts that may not resolve the issue.

When checking wheel sensor output look for nothing less than 100 millivolts. Depending on wheel rotation speed the output will vary in a range from at least 100mv to approximately 1 volt.

On the drive cycle mentioned earlier: it is defined as:

Starting vehicle
Driving vehicle faster than 10 mph
Stopping vehicle
Turning ignition to off

[mikeswaggs]

Thanks for your help. I had wondered if the system would want to see some wheel speed, etc. before clearing the codes. I had seen a similar situation on an old Buick Skylark when we changed the master cylinder. The light did not turn off until we drove it around for a while. I am going to try the continuity test first, then the hub, and take it for a ride. I don't have time to work on it for a couple of weeks, so when I do, I'll update the thread. Hopefully it'll be good news.