Jim Grant's Tech Tips
GM Anti Lock Brake Recall
My ’00 GMC K1500 4x4 pick-up truck has anti-lock brakes. I recently heard that there was a recall on my vehicle for an antilock brake problem. My anti-lock brakes were doing very weird things. It started off with the anti-lock pump running and the brake pedal dropping when I was parking the truck. I took it into the shop and was told the brakes were fine and that the anti-lock brake computer did not have any codes. As time went on the problem got so bad that the truck would not stop while driving into a parking space. I would have to throw the shifter into park. This made all kinds of noises, but at least I did not hit anything. What was strange is that the brakes worked fine at higher speeds. It was only when I got below 10 MPH that I would lose my brakes and couldn’t stop my truck. After spending “a lot of money” going to different dealers and garages and getting no where, I found a shop that knew what the problem was and fixed it. The part I didn’t understand was, they told me it was rust that was causing some sensor not to work right. My question: is this recall for the same problem my truck had? If it is can I get any of the money back I spent trying to get this problem fixed? Will it happen again and if so is it covered by this recall? Last, what was happening to cause my truck to lose brakes like that?
At this article’s time & date I have not seen documentation regarding the recall you’re describing. Doesn’t mean it isn’t happening, just means I cannot make a statement without documentation of a recall. With that said, I can tell you that your complaint is not uncommon and I would not be surprised at all if there is a recall. Getting your money back? In general, if you’ve spent money repairing a problem prior to the announcement of a safety recall there will be provisions for a refund of some sort. But, it is important that you have your documentation of the repair and/or parts that were replaced. Will it happen again? If it’s the problem we’ve been seeing, it is probable and more likely to occur or reoccur if your vehicle is operated in the northern 13 states and Canada. This leads us to your last question, what is causing the problem? If we’re all on the same page, the cause for the problem is due to rust. Vehicle’s equipped with 4-wheel anti-lock brakes have a speed sensor located at both front wheels. At each wheel there is a gear with teeth that spins with the wheel as it turns. This is often called a toner ring. Mounted about 5 or 6 strands of hair away from the teeth of the toner ring is a wheel speed sensor. As each tooth passes the sensor an electrical signal is generated. So as the wheel turns and each tooth of the toner ring passes, the sensors sends a signal to the anti-lock brake computer. Because the anti-lock brake computer has a sensor at each wheel it can compare the information from the sensors to determine wheel speed. The problem we’re seeing is being caused by rust getting under the wheel speed sensor and lifting it up. Here’s a little piece information that is critical in understanding why a little bit of rust becomes a big problem. Earlier, I mentioned hair strands. The wheel speed sensor creates its signal as the teeth on the toner ring pass by. The distance between the teeth of the toner ring to the sensor affects the strength of the signal. All you have to do is move that sensor away from the toner ring a hair strand or 2 and the signal becomes weaker. If the rust gets bad enough at low speeds the signal is too weak and when you step on the brake, the anti-lock computer thinks the wheel is stopping when it isn’t. The fix for this problem is to remove the wheel speed sensor and clean the rust off the sensor and from the mounting surface. That part is easy to say, it takes more time than that because you have to remove the tire, brakes and rotor to get to the sensor. Not to mention often times that the bolt that holds the sensor in is so rusty you can’t get that darn thing out without it becoming a production. Once free of rust and the wheel speed sensor correctly positioned the anti-lock brake system will be working as it should.