My truck's a 2001 GMC 2500HD 6.0L. Randomly, upon start-up the ABS and parking brake lights come back on immediately after going out and then stay on until key off. To put it another way; when you start the truck all the lights come on like normal, then they go off and in less than a second the ABS light comes back on followed by the PKB light. This has been happening intermittantly for some time and usually the lights would not stay lit after the next restart, but the frequency and persistance are increasing. I just started it six times in a row and the lights stayed on every time.

The lights never go from off to on while driving, only at start up.

I've cleaned the EBCM grounds and checked all the connectors. The battery seems strong and the connections are good. I live in Phoenix, so basically nothing corrodes.

Any ideas?

Thanks,
John

Brake fluid level, parking brake applied?

Thanks for the reply. The fluid level is good, I pulled out the fluid level sensor and cleaned it and it's contacts. The parking brake is not applied.

I should also add that there is no message in the DIC and no warning chimes.

Any chance it could be a problem inside the fluid reservoir with the fluid level sensor??

Thanks
John

Have you checked the front wheel sensors and the sensor in the transfer case?

Im not 100% but i ran into something like this about 2 months ago with no codes and both lights being on, I "thought" it had something to do with an internal fault in the brake controller.. But again im not 100%, it is ringing a bell for me though..

The speedometer reads correctly and doesn't seem to have any problems, which makes me think the speed sensor in the T-case is probably okay, right?

I haven't checked the ABS wheel sensors (except to look at the cables without removing the wheels), but I wasn't sure if they would set the lights before the truck is even put in gear and moving. And, the lights never come on while driving.

If you have one , what is the voltage on the voltage meter while this is going on, sounds like poor battery voltage to me . The more you start it , the lower the voltage would be and the lights would stay on longer. just my thoughts Charlie

Cranking voltage is ≥10.5 measured on a big analog meter. Crank speed is good.

I'm pretty certain this problem has persisted through at least one battery replacement.

I just got back from running errands with two stops. The lights were on the whole time. Restarted to check the voltage and the lights went out. Restarted three more times, still the lights stayed out. :confuzeld

Thanks for the thoughts,
John

The speedometer reads correctly and doesn't seem to have any problems, which makes me think the speed sensor in the T-case is probably okay, right?

I haven't checked the ABS wheel sensors (except to look at the cables without removing the wheels), but I wasn't sure if they would set the lights before the truck is even put in gear and moving. And, the lights never come on while driving.


I'm always looking back to what happened to me . It's easy to eliminate the transfer case speed sensor since it usually go haywire when the reluctor comes into contact with it. That happens from internal damage that allows the main shaft to move where the reluctor comes into contact with the end of the speed sensor. You can either eliminate that from a cause by either removing the speed sensor and looking at the end of it to see if any contact has been made, or you can grab the driveshaft where it comes out of the transfer case and move it up and down to see if there is any movement(play). If that isn't the problem you are lucky enough for it to be something else. Any oil on the transfer case?

I haven't pulled the speed sensor though. I guess I'll do that later if it comes to that.

Thanks,
John

Speed sensor looks fine. Driving it around more today, this morning the lights were staying on, this afternoon they're off. I can't figure out any pattern. Nothing else seems to change or have any effect one way or the other.

John

Did they stay off after you checked your speed sensor? Just wondering if it may have been the connector.