happy holidays everyone.

my grandmas 2000 blazer soon to be mine drives fine most of the time but the (ABS) light is always on. today i was driving around and the brake started pulsating and i know that could mean that the disc needs to be re-finished and then my grandma said that she was driving along once and the pedal went to the floor and she had to pump it to stop. i know the ABS light could be from a bad wheel bearing but i checked that and its good and it has plenty of brake fluid.

anyone know of anything i could check? any help would be appreciated.

thanks and looking forward to the help.

 

You will need a scan tool capable of retrieving ABS DTC's. Brake pedal going to the floor could be a problem in the ABS unit, and the DTC that's in memory could be a clue as to what's wrong. The ABS light could also be a problem with a wheel speed sensor, and if the vehicle has 4WD, the sensor is part of the wheel bearing assembly.

 

it is 4x4 so does that mean even if the bearings arent bad themselves i still might have to replace them because of the sensor?

 

Yes. The tip of the sensor needs to be a certain distance from the reluctor wheel, (tone ring) inside the hub assembly, usually ~.003". If the air gap is too close, or nonexistent, the sensor will be destroyed when the tip contacts the reluctor when it rotates. If the gap is too large, the sensor will not generate a signal. Each sensor is "fitted" with stainless steel shims during the manufacturing process that position the sensor where it needs to be. Some vehicles use an exposed reluctor attached to the CV joint. This allows the air gap to be checked/adjusted using a feeler gauge. Sensors are available seperately, but it's not a recommended repair, for obvious reasons.

There's a GM TSB that addresses the possibility of rust buildup between the sensor and the hub. If this occurs, the rust pushes the sensor outward which increases the air gap and the signal becomes erratic. In the early stages, it does not set a DTC in memory or turn the ABS light on. As the sensor moves farther away from the reluctor, eventually the light will come on and a DTC will be set in memory. The sensor can be removed and the rust cleaned off, and if this is the problem, it's a cheap fix.

Here's a link to the TSB:
http://ww2.justanswer.com/uploads/GM...s_bulletin.pdf

 

Check out the tech article section . At the top of the index (link in my signature below) there is an article discussing testing of the sensor to determine if the air gap is correct.