Gmc Antilock Brake Issue

putter44 · August 18, 2011

I've got a 2002 GMC Sierra and have had the low speed antilock brake issue that I know many others have had. I replaced the wheel speed sensors and still am having the problem. The wheel bearings are good. The only thing I think I may have not done correctly is cleaning the seat of the sensor well enough. I'm going to take it all apart tonight again and make sure that it is as clean as possible. I know it's important to keep debris out of the sensor hole while it's out but I noticed on one post that someone said to clean the inside of the housing as well. I have not done this because I know it's all sealed and greased and I don't want to introduce anything that will damage or degrade the lubrication inside. Does anyone have any other suggestions while I've got it apart?

Wires · August 18, 2011

I've got a 2002 GMC Sierra and have had the low speed antilock brake issue that I know many others have had. I replaced the wheel speed sensors and still am having the problem. The wheel bearings are good. The only thing I think I may have not done correctly is cleaning the seat of the sensor well enough. I'm going to take it all apart tonight again and make sure that it is as clean as possible. I know it's important to keep debris out of the sensor hole while it's out but I noticed on one post that someone said to clean the inside of the housing as well. I have not done this because I know it's all sealed and greased and I don't want to introduce anything that will damage or degrade the lubrication inside. Does anyone have any other suggestions while I've got it apart?

The GMT-800's and even vehicles from other manufacturers use the same crappy ABS pump controller. It's located on the frame rail on the driver side.

Your controller has most likely died (VERY common on these vehicles). You can google, and there is a place that will fix the faulty driver in the controller, and fix your problem. In my case, I couldn't get the rusted bolts loose, so learned to live with it. Wasn't a big loss, since the ABS in my '00 was a POS anyways. 1000x improvement in my GMT-900.

ChevyTech77 · August 18, 2011

The GMT-800's and even vehicles from other manufacturers use the same crappy ABS pump controller. It's located on the frame rail on the driver side.

Your controller has most likely died (VERY common on these vehicles). You can google, and there is a place that will fix the faulty driver in the controller, and fix your problem. In my case, I couldn't get the rusted bolts loose, so learned to live with it. Wasn't a big loss, since the ABS in my '00 was a POS anyways. 1000x improvement in my GMT-900.

The ebcm's did not cause the unwanted abs activation that the OP is describing here. They did cause the pump motor to run non-stop in the early GMT-800 years yes, but unwanted abs activation? No.

To the OP,

Clean the sensor mounting surfaces down to bare metal. If you have a dvom, assure that you have at LEAST 350 ac mv of output from each of the wss's when spinning the hub bearing by hand when you're done. If they are both capable of 350 ac mv, without having to spin the hub like a mad man, then you are good to go. If lower than that? Keep cleaning the surface. Again, a good rule of thumb is to just clean the surface until you are down to good clean bare metal.

Wires · August 19, 2011

The GMT-800's and even vehicles from other manufacturers use the same crappy ABS pump controller. It's located on the frame rail on the driver side.

Your controller has most likely died (VERY common on these vehicles). You can google, and there is a place that will fix the faulty driver in the controller, and fix your problem. In my case, I couldn't get the rusted bolts loose, so learned to live with it. Wasn't a big loss, since the ABS in my '00 was a POS anyways. 1000x improvement in my GMT-900.

The ebcm's did not cause the unwanted abs activation that the OP is describing here. They did cause the pump motor to run non-stop in the early GMT-800 years yes, but unwanted abs activation? No.

To the OP,

Clean the sensor mounting surfaces down to bare metal. If you have a dvom, assure that you have at LEAST 350 ac mv of output from each of the wss's when spinning the hub bearing by hand when you're done. If they are both capable of 350 ac mv, without having to spin the hub like a mad man, then you are good to go. If lower than that? Keep cleaning the surface. Again, a good rule of thumb is to just clean the surface until you are down to good clean bare metal.

My bad, missed the low speed issue. You can also have the pump driver fail so you never get ABS as well (not always on).

If the speedo is functioning, then there is an issue with one(both) front wheel speed sensors.

asc08 · August 19, 2011

I had the same issue. Cleaned the WSS mounting area with a wire brush and a small scraper, put it all back together, still activated at low speed.

Ended up really going at the mounting surface with a dremel tool, got it down to bare metal, re-installed the sensor (this time I did the voltage check) and all was good. Be sure to use some corrosion protection on the newly cleaned surface.

To protect the opening from getting debris in it, I used a foam ear plug, and stuffed it in the sensor opening, it was a great recommendation from another poster on this site.

Someone else on this site was a bit confused, but 350 millivolts is .350 volts, so if your volt meter does not read in millivolts AC, just set it for the low voltage reading, and you should be good to go.

oppirs · August 22, 2011

I had the same issue. Cleaned the WSS mounting area with a wire brush and a small scraper, put it all back together, still activated at low speed.

Ended up really going at the mounting surface with a dremel tool, got it down to bare metal, re-installed the sensor (this time I did the voltage check) and all was good. Be sure to use some corrosion protection on the newly cleaned surface.

To protect the opening from getting debris in it, I used a foam ear plug, and stuffed it in the sensor opening, it was a great recommendation from another poster on this site.

Someone else on this site was a bit confused, but 350 millivolts is .350 volts, so if your volt meter does not read in millivolts AC, just set it for the low voltage reading, and you should be good to go.

Well it just happen to me, Today!! Almost had an accident do to this slow speed activation on dry pavement. It happened 3 times before today but at stop signs with no traffic. But I still went a 1/4 way into the intersection, ARRRG! Not every braking did this ABS act-up on.

Normally from day one since I bought new in 2003 the brake pedal was kinda soft, but today that pedal was rock hard only moving down a faction of an inch, ABS vibrating away & I couldn't stop her until I thru it in Neutral. After this heart in the throat feeling I pulled over and yanked the 60amp ABS circuit breaker. Now my brakes act normal!!

I have never been a big fan of ABS. (Driving in Chicago in the winter before ABS you learned to pump the brakes very quickly)

I had one wheel bearing replaced for bearing failure, a few years back and yes the ABS did light a few times before replacement. Not the last three times or today the ABS light didn't light at all, except when I pulled the circuit breaker. Now I'll check into what you guy's did & read for 350+mv ac. Then try cleaning the surface areas. I also heard that the VSS could be bad. I think it was WIRES that said if you still have a speedo (which I do) Look at the front sensors.

I gather WSS means wheel speed sensor? Are these sensors removable and do you grind to aid in a better ground?

asc08 · August 23, 2011

OPPIRS -

Yes, WSS means wheel speed sensor. There is one on each front hub. Apparently what happens is the surface of the hub corrodes, pushing the sensor slightly out of the hole.

What you need to do is clean the mounting surface down to bare metal, to remove the corrosion that has built up. The first time I did it, I used a wire brush, and that was not enough. I took the short cut and did not check the voltage, which was a bad move.

I looked into new sensors when the first repair did not work, and, for my particular truck, it would have been cheaper to replace the whole hub, with sensor.

So, I tried it again. Checked voltage (less than 100 millivolts), removed, used a dremel tool to clean the surface to bare metal, coated the area with grease (for some corrosion protection), re-installed, checked voltage (over 350 millivolts).

When I cleaned the surface, I stuffed a foam ear plug in the hole to keep the crud out.

I did not get an ABS light when this happened. I do not believe that the grinding is for ground, but for proper alignment and position of the sensor. I would not use the term 'grind', but rather 'clean' to bare metal. My fear is that grinding tends to remove a lot of material, and if the sensor is thrown off by a little corrosion, it may get thrown off in the opposite direction by removing too much material.

Since you need to remove the caliper and rotor, it may be a good time to replace pads and or rotors while you are in there.

The whole operation took about an hour or so.

ChevyTech77 · August 23, 2011

You are not grinding the surface to facilitate a ground, you are grinding it down to create the correct air gap between the sensor and the tone wheel that is inside of the hub bearing. Too close though, and the sensor will hit the tone wheel.

Overclock · August 23, 2011

I don't have a dremel; Any recommendation on what to use to clean the surface without buying one?

I used wire brush first time and it didn't work.

ChevyTech77 · August 23, 2011

A hand file would be the only other thing that I could think of, that would work, other than a Dremel type grinder with a deburring bit.

Kirkathon25 · August 23, 2011

i just manned up and replaced the wheel bearings after many unsuccessful attempts at cleaning those sensors, i got the american made wheel bearings and havent had a problem yet, another suggestion is yanking the fuse out lol i did that for a while too, so nice of gm to issue a recall on those wheel bearings but wont pay to replace them

ChevyTech77 · August 23, 2011

i just manned up and replaced the wheel bearings after many unsuccessful attempts at cleaning those sensors, i got the american made wheel bearings and havent had a problem yet, another suggestion is yanking the fuse out lol i did that for a while too, so nice of gm to issue a recall on those wheel bearings but wont pay to replace them

No offense but if the cleaning procedure is done correctly, and the hub bearing doesn't have any play, and the unwanted abs activation IS from the FRONT wheel speed sensors as confirmed with scan tool data, cleaning the sensors will work every time. I've done thousands of them, literally. Still do, from time to time as well.

Kirkathon25 · August 23, 2011

none taken, just what i did after trying cleaning them based on explanations in type lol, i suppose i could have benefitted from a video, it all just seemed iffy to me so it was about time for wheel bearings anyway.