GM 2500 ABS sensor

[kamccarthyinc]

Looking for suggestions. I have a 2002 GMC 2500 HD (8.1L gas) 4x4. It appears my driver's side ABS sensor is gone, because when I slow down to under 3mph, it triggers quickly. I have heard countless nightmares of people who have tried to change this sensor. Apparently, this is a very popular issue with the GM's, and finally now you can puchase only the sensor without the hub assembly at NAPA. I'm told if I can't get the sensor out, I'll be buying a new hub assembly. Any tips, suggestions, etc. are greatly appreciated.

[Rbeckett]

I have replaced a few of those hubs due to sensor failure and it is not an inexpensive undertaking. If NAPA has a seperate sensor, and you can succesfully remove the old one it will be a money saver for sure. If you do attempt to remove it I would start a day or two early dousing it with PB Blaster or some other good penetrating oil. WD40 is generally too thin to be of much help on one that is really stuck, Blaster or deep creep seem to work the best. Once you have liberally bathed the sensor, tap it gently and attempt to pull it as square to the bore as possible. Some will slip right out, others will be there forever. If I remember that hub was about 525.00 when I was buying them from NAPA, the dealer was close to 800.00. I never had an issue with the NAPA failing early so it was a decent replacement part that has given good service. Glad to see someone addressing the sensor issue finally... Good luck and hope it helps.
Bob

[kamccarthyinc]

Bob, thanks for the advice. I'm hoping to get that sensor out without incident. Fortunately, it seems NAPA as well as other autoparts stores have come down significantily on GM replacement hubs. I forget where I got one quoted, but it was under $300 for a Timken which is pretty good. Needless to say, I think I have nothing to lose by trying to work the old sensor out first. The truck only has 60k on it and the hub has does not have any play or noise which would indicate wear, so if don't have to replace it that would be nice.

[dabar39]

I just had a customers truck here (same as yours 02 2500 HD 4x4 but he had the 5.7 in it.) with a bad abs sensor on it, a new sensor was $127.00 but the whole hub assembly was only $143.00 with the new sensor attached to it. Dollars and cents wise it was better to just change out the whole hub assembly.

As suggested make sure you hit the mounting bolts with some penetrating oil before trying to take it apart. I broke one of the bolts off that holds the wiring harness to the caliper, had to drill it, easy out and then replace the bolt, added an hour onto a job that I hadn't counted on. A little never-seize on the reassembly should keep everything good for the next time it has to be taken apart.

[kamccarthyinc]

Thanks dabar39. I'm by no means a mechanic but I feel I could handle the whole hub replacement, but don't want to if I don't have to.

[angrysam]

There was a recall on this a few years ago. You might want to check with your local dealer and see if yours falls under it.

GM found that it's not always the sensor that is the problem. Rust builds up between the sensor and the hub causing the sensor to lift slightly. This increases the air gap between the sensor and the tone ring causing the low speed activation you've described.

GM had us pull the sensors, stuff cloth down the sensor hole, and clean the hub area where the sensor mounts. Once all corrosion was gone we'd apply a type of rust converter to the hub, standard chassis grease on the sensor and reinstall it. This fixes them completely.

If you're short on cash or if your truck is not part of the recall you could try this. If you can get the money together then I'd just get the whole hub assembly as it comes with the sensor. If your truck has higher mileage then your hubs may be starting to get loose anyway which will also cause the low speed ABS activation.

[kamccarthyinc]

Thank angrysam. I have gone round and round with my dealership over this. I actually learned of the recall from my private ASE mechanic who works on my vehicles, because he didn't want to take my money for something GM could fix for free. Unfortuately, I was told by one service manager that my truck did not conform to the recall, and another manager told me that no such recall ever existed. I called GM customer service and they confirmed that there was such a recall, but it is now closed and my truck doesn't apply. So, what your saying, is that you didn't replace the sensor, rather scuffed it clean, and replyed grease to the hub? Is there anything you can pass along that would help get that sensor out in one piece without destroying it?

[angrysam]

Here's the official recall info and procedure:

Bulletin No.: 03-05-25-007D

Date: May 01, 2009

Subject: Antilock Brake (ABS) Activation At Low Speeds (Clean Wheel Speed Sensor Mounting Surface)
Models:
2002-2006 Cadillac Escalade, Escalade EXT
2003-2006 Cadillac Escalade ESV
1999-2006 Chevrolet Silverado
2001-2006 Chevrolet Suburban, Tahoe
2002-2006 Chevrolet Avalanche
2003-2006 Chevrolet Express
2007 Chevrolet Silverado Classic
1999-2006 GMC Sierra
2001-2006 GMC Yukon, Yukon Denali, Yukon XL, Yukon Denali XL
2003-2006 GMC Savana
2007 GMC Sierra Classic
2003-2006 HUMMER H2

Supercede:This bulletin is being revised to add the 2007 Silverado/Sierra Classic models. Please discard Corporate Bulletin Number 03-05-25-007C (Section 05 - Brakes).

Condition

Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.

Cause

The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.

Correction

Measure AC voltage and clean the wheel speed sensor mounting surfaces.
1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in the General Information sub-section of the Service Manual.
2. Disconnect both the front wheel speed sensor connectors at the frame and harness.
3. Place a Digital Volt Meter (DVM) across the terminals of each wheel speed sensor connector.
4. Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's. If the reading is less than 350 ACmV's, remove the wheel speed sensor. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
5. Plug the wheel speed sensor bore in order to prevent debris from falling into the hub during service.
6. Clean the wheel speed sensor mounting surface using a wire brush, sand paper, emery cloth, scotch brite, or other suitable material. Be sure to thoroughly clean the wheel speed sensor surface. There should be no rust or corrosion.
7. Check the sensor head to determine if it has been warped/distorted due to the corrosion build up or other causes. Check the mounting surface on the sensor head for flatness by placing it on the edge of a metal machinists scale or other suitable straight edge to measure the flatness. Check the sensor for flatness in multiple (minimum 3) positions/directions. If the sensor head is distorted, replace the sensor.
8. Apply (spray) two thin coats of the specified rust penetrating lubricant (corrosion inhibitor) to the complete sensor mounting surface on the bearing hub. Allow to dry for 3-5 minutes between coats. Use ONLY Rust Penetrating Lubricant, P/N 89022217 (in Canada, P/N 89022218).
9. When the corrosion inhibitor is dry to the touch (about 10 minutes), apply a thin layer of bearing grease to the hub surface and sensor O-ring prior to sensor installation. Use ONLY Wheel Bearing Lubricant, P/N 01051344 (in Canada, P/N 993037).
10. Install either the original sensor or a new one in the hub. Ensure that the sensor is seated flush against the hub. Refer to the applicable Wheel Speed Sensor Replacement procedure in the ABS sub-section of the Service Manual.
11. Place the DVM across the sensor terminals and recheck the voltage while rotating the wheel. The voltage should now read at least 350 ACmV's.

[angrysam]

As has been suggested soak the sensor area down really well with some type of penetrating lube. Everyone has their favorite, JB-80, GM's Heatvalve Lube and Schaeffer Penetro 90 all tie for mine.

I've never been to RI but I imagine you have rust issues as bad as we do in MN. Lube it really good, remove the sensor bolt and slightly twist the sensor with pliers. It sounds weird but if you're really paying attention you'll be able to feel if the whole sensor is twisting or if only the top is twisting. If the whole thing is twisting then twist a little more, keep working it side to side while you slightly pull up.

Be sure to give the sensor a firm tap with a plastic hammer or flip a screwdriver upside down and tap it to be sure that the sensor is sitting flush.

You don't see it as much with the 3/4 tons as you do with the 1/2 tons but the rotors have been known to stick to the hub flange due to rust build up. Lube that area really good or you'll beat the hell out of your rotors trying to remove them. Let it sit overnight if you can.

Here's where you're going----

[bollinger660]

if you pull the sensor out and what normally what happens is the plastic around the out side of the sensor gets rusted to the hub and breaks off. i have in the past cleaned the hub and sensor just like gm recommends and put back together with no problem. the plastic part is just a cover. grease it all up good. i have done this job this way countless times. good luck with those rotors also. they can sometimes be a pain in the a$$.

[kamccarthyinc]

Angrysam, I need to remove the hub assembly from the truck to do this proceedure? I would assume so if I need to clean the hub. Thanks again for your help.

[kamccarthyinc]

Angrysam, I need to remove the hub assembly from the truck to do this proceedure? I would assume so if I need to clean the hub. Thanks again for your help.

[angrysam]

No. The sensor is right on top of the hub and easy to get at. Pull the caliper and rotor and undo the rectangular clip for the sensor wiring at the upper ball joint (squeeze the ends together with pliers). This will give you enough room to pull the sensor out. I always pulled it out and pushed it through the backing plate so it was out of the way. Shove something down the sensor hole (I used a little piece of foam rubber) and clean the area around the sensor (I used a 1" diameter wire brush in my cordless drill).

Don't know if I mentioned it earlier but check your hubs before you pull the wheels. If they're loose at all then replace the hub because they're only going to get worse. In case you're unfamiliar-- Jack under the lower control arm, hands at 12 and 6 on the tire, push/pull with your arms and see if anything is loose.

[monte433]

I just did this last night most of the time the sensor is fine, the rust builds up under the sensor and pushes it up causing it to read different than the other side and set off the ABS.