Anti-lock brakes too sensitive

[Heeb]

I'm disappointed with the anti-lock brakes on my 2000 GMC Sierra 1500 with the Z71 package. When there are bumps in the road and I need to slow down or stop, the anti-lock system kicks in, and I've got to get off the brake and back on it again to slow the beast down. On one occassion earlier this year, I actually doinked a car that was stopped in front of me at a light. The surface was completely dry and free of debris, but the concrete was a little rough. Has anyone found a way to adjust the sensitivity of the anti-lock system? Lowering my tire pressure might help, but I don't want to jeapordize tread-life.

[PK55Z85]

"sensitivity"....this isn't Cosmo dude
just teasing...there is no adjustment for the abs
it's either working or not...now you might have a wheel speed sensor reading erratic or a wiring harness with some kind of open or short giving the control module erratic signals
it also sounds like it could be a normal condition...depending on your driving habits. it's not abnormal for this type of condition to happen while stopping over bumps at a quick rate of decell.
if a wheel momentarily loses traction. but you should NEVER take foot pressure from the brake pedal...in doing that your telling the computor there is no more need to slow down...thats not the trucks fault.

[GMCTech]

You are experiencing what GM calls low speed ABS activation, and is quite common and not so cheap to fix.

Let me explain:

The wheel speed sensors are built into the hub. As the hub/bearing wears out, it allows the reluctor (pick-up) wheel to move away from the wheel speed sensor. This causes too much of an air gap, and the wheel speed sensor sends an erratic signal to the EBCM (electronic brake control module).

This in turn looks like a wheel slip and the ABS is energized and engages. This usually happens at low speeds, because the signal is more erratic at lower speeds.

The only true repair is to replace the bad wheel bearing/hub assembly. GM does explain a removal and readjustment procedure, but I haven't seen that fix last more than a couple months before the same concern re-arises.

So, plan on buying one or both hub bearing assemblies to resolve your issue.

Hope this helps.

[Heeb]

I took my truck to the dealer while the truck was still under warranty (a couple of months ago) and they explained that there was nothing that could be done. Now, I'm beyond my 3 years and 36K warranty and it sounds like the problem is mine to work out unless I can talk them into fixing it since I asked them to check it out before the warranty expired. Thanks for the feedback!

[PK55Z85]

if you have proper documentation...copy of a repair order-invoice where the dealer inspected-checked for this concern...they still should be able to cover it. if there really is somthing wrong...but it has to be within a reasonable amount of time, don't wait 6 months then go back. go for a test drive with the shop foreman or tech, so you can verify concern with them in the vehicle.

[Heeb]

I'm scheduled to take the truck to the dealership tomorrow for them to check the tolerances on the hub bearing assemblies. They've agreed to check them out under the warranty since they weren't inspected when I'd expressed concern about the ABS system previously. I'll let you know what they find!

[Heeb]

The dealership offered to replace the hub assemblies as long as I paid the labor only after I'd called GMC customer assistance and told them about the experience I'd had with the dealership in the past regarding this issue, but I thought that they should pay for parts and labor, since I'd originally brought it up before the warranty had expired. After spending almost an hour and a half on the phone with GMC customer service (they did a fabulous job of listening to my explanation of the problem), they agreed to take full responsiblity for the repair. Thanks for all the advice guys!

[gregborz]

Finally I have found someone else with the same deal. My brakes lock and the ABS sound kicks in at 8mph down to 4mph. The thing only has 24,000 miles on it and the dealer just replaced the sensors, but that didn't help at all.

Any ideas? My brakes are bad, but should that matter here? It is so weird that the low speed braking is messed up. My truck is only a 2002.

[GMCTech]

Like I had posted above, you will need to replace one or both of your hub assemblies.

I don't know what kind of shop just replaced the sensor, that isn't even an option in the diagnostic trouble chart.

Find a dealership that has a clue as to what they are doing. I think that every dealership has dealt with this problem a ba-zillion times. I know we have done COUNTLESS hub replacements and continue to do them day after day.

Hope this helps.

[gregborz]

Originally Posted by GMCTech

Like I had posted above, you will need to replace one or both of your hub assemblies.

I don't know what kind of shop just replaced the sensor, that isn't even an option in the diagnostic trouble chart.

Find a dealership that has a clue as to what they are doing. I think that every dealership has dealt with this problem a ba-zillion times. I know we have done COUNTLESS hub replacements and continue to do them day after day.

Hope this helps.

Thanks SO much. I am going to take this into the dealer and show them. Your shop wouldn't be anywhere in south Florida, would it? Another question- would the hub assembly be covered under warranty for my truck that is less than 3 years old and 24,000 miles?

[Heeb]

The hubs should be under warranty. My warranty period had expired, but since I'd documented the problem with a service call within the warranty period, I had enough leverage to have GMC pay for the parts and labor.

[gregborz]

Originally Posted by Heeb

The hubs should be under warranty. My warranty period had expired, but since I'd documented the problem with a service call within the warranty period, I had enough leverage to have GMC pay for the parts and labor.

Thanks so much guys. I am heading to the dealer right now. You 2 and this forum, have been so much more helpful than anything else, including the dealership where I bought the car and the dealership where I am trying to get it fixed!

[twshank]

I have this prob. on a 98 K1500 w/ 32K. Is this the same problem? Everyone 'round here thinks it's the ABS module.

[gregborz]

Originally Posted by twshank

I have this prob. on a 98 K1500 w/ 32K. Is this the same problem? Everyone 'round here thinks it's the ABS module.

I had my ABS sensors replaced and it didn't change a thing. I am going to pick my truck up today from the shop after they replaced the hubs. I think that is the fix. Don't bother replacing the sensors for this problem.

[twshank]

Thanks everybody. The hub thing boggles the mind. If I did what an independent shop said, I would be buying the $600 main brain. If that didn't fix it, don't know whether I would shoot the mechanic or the truck.