Does it wait until you're moving before throwing the code? If so it's probably a speed sensor. One on left front hub, right front hub and either one for the rear or possibly two for the rear.

Ted

 

No, the lights come on before you are even moving, still in Park. They will stay on after you are moving until you shut off the engine and re-start.

 

Does the ABS pump run whenever you apply the brakes? Does it never come on? Have you checked all fuses?

Do use the parking brake often, or never?

Sorry for all the questions. Just trying to get a feel of what's going on.

Yes it might help to clean the connector and also the ground stud near it.

Ted

 

Ted,
1. Since the ABS unit is under the vehicle, I can't tell if the ABS pump is running or not, if ever. We don't get much snow here, so I've never had an instance to activate the ABS.
2. Haven't checked fuses yet.
3. I typically park on level ground so I rarely use the parking brake.

I went ahead and cleaned both connectors on the unit. My GM factory schematic doesn't show any ground stud nearby, nor did I see one while I was underneath the vehicle.

One other thing to mention. I like to turn the ignition on and wait until the fuel pump has stopped running before I start, insuring that the fuel rail pressure is up to snuff. If everything is going OK, the ABS and Brake lights will go out before I even hit the starter. If they are going to cause a problem, they will continue to stay one even after I start and before I depress the brake pedal for the first time.

 

Every time you turn the ignition to run the vehicle runs a self diagnostic test on the system. When it's staying on that means there is a current fault. Next time the lights come on and stay on check for codes and post your results. Sounds like a poor connection somewhere though since it's intermittent.

 

I just made a 600 mile trip this weekend and the brake light and the ABS light came on a few times, always at start-up. I just remembered something that my be a cause. About six months ago I replaced the front wheel bearing assemblies, which included included new tone rings and sensors. Could one of the sensors be intermittent causing the problem?

It's raining today, but tomorrow, I hope to check the resistance readings between the old and new sensor coils.

I replaced the bearing assemblies with genuine GM parts, for what that's worth.

 

Its better to check the AC signal output from the sensors instead of getting resistance readings. I use a digital scopemeter.
Clean the grounds first. Very easy. Under the driver side frame rail, by battery, etc.
If that doesn't fix it, you may have no choice but to drop the ABS brain under the driver side frame and reflow the relay pin solder joints.
Or just send it out for repair.
Good luck.

 

The problem occurs during initial check out before the vehicle is moving; hence, there will be no AC signal to observe from the sensors. I suspect it is either a bad connection or a sensor coil out of tolerance.

 

bazar01, you got my curiosity going. I got my oscilloscope out and checked both sensors while turning the hub. Both showed signals of the same amplitude. However, both of the new sensors measured higher coil resistance that the old sensors. Since I was halfway there, I went ahead and re-installed the old sensors.

No re-occurrence of the ABS light. We will see how things go over the next week or so.

 

bazar01, the lights came back on today. Is there a video on the internet which covers reflowing the relay pin solder joints?

 

post #7 on this thread.

http://www.gmtruckclub.com/forum/threads/abs-module-removal.92093/

 

Thanks for the link. I'll give it a try tomorrow. At least the solder joints are conventional. The Bosch units that Ford uses mate aluminum wire with copper PC boards - never a good combination.

 

You can always send in the abs unit here for $99

https://circuitboardmedics.com/kelsey-hayes-325-abs-module-repair-chevy/

 

Success! I took the module out Friday and opened it up. I've been repairing TVs since I was 15 and have made a lot of money repairing cold solder joints. The bad joints on this board really stood out. I re-soldered them and touched up all of the solenoid coil connections.

The tan stuff on the metal top is thermal heat sink compound. Corresponding to each of the pads on the printed circuit board is a transistor (on the other side of the board). The tan stuff helps transfer the heat from the transistors to the metal cover. It is important the apply a little bit of fresh thermal heat sink compound to each of these pads; otherwise, you may lose a transistor down the line due to overheating.

Thanks for your tips and suggestions.

 

I replaced one or two of mine a while ago. I can only remember there were rust issues at the sensor, sensor connections, cable wear, etc. Mine was pretty beat up from the Midwest winters, salt , etc. when you looked close. I do a lot of highway driving and it gets messy.

 

My Suburban spent its first 5 years in Central Florida (Gainesville) and the rest of its life in the Atlanta area, so no rust issues. In fact, when I saw the old sensors after I replaced the front wheel bearing assemblies, the sensors looked pretty good. I had gone back to the old sensors while troubleshooting the ABS and Brake lights and still have them on the Suburban.

All the lights are still staying off when they should!

 

I had an 01 Suburban with the exact same problem. It's your ABS module. If I remember correctly it's under the front passenger seat on the undercarriage. Maybe along the frame rail. It's exposed to the elements so maybe that's why they fail. Read many posts of Suburbans within that model year having same problem. I tapped mine with a crescent wrench and brushed it off with a bristled brush. Problem went away then I sold it.

 

He already got the module out and resoldered. It is fixed.

 

Hi...it seems it's exposed to the elements so maybe that's why they fail. Read many posts of Suburbans within that model year having same problem. I tapped mine with a crescent wrench and brushed it off with a bristled brush.