ABS engages early

[ghostdog]

I have a '99 GMC sierra 4x4 new body style and sometimes it feels as though the ABS kicks in on dry roads at 5 miles/hr. It is so bad that it seems like i'm gonna hit the guy in front of me. I took out the fuse for the ABS and it does not happen (but the ABS and BRAKE lights are on all the time). Anyhow I am gonna take it into the dealer on sat. and was wondering if anyone has had this problem.

 

thanks,

mike

[RyanbabZ71]

Is the abs pump constantly running?

 

The abs sensor might be dirty???

[GMCSierra04]

Most ABS systems run self diagnostic checks during initial start up and another when the vehicle is moving at 3-8 mph. The soleniods and pump may be heard during these tests but if you feel that it is over sensitive, I would check the toothed sensor rings and make sure no teeth are missing or damaged. Also check where the speed sensor mounts, I don't know if the air gap is adjustable or is just fixed but look into that too. The speed sensor has a small magnet inside and the toother wheel is there to "disturb" the magnetic filed, producing an analog AC signal which will then travel to the ABS computer, I wouldn't think dirt would mess anything up but not 100% sure on that one. There also might be a problem with the pulse motor but the best thing is to take it so it can be scanned to figure out exactly what the problem is. Hope some of this helps.

[electromag8]

My 99' seems to be sort of like you are 'splaining as well. Especially at the speed bump right before my house. You trun right just past it, and you have to practically stop at it or the ABS kicks on. It can become very uncomfortable to say the least.

 

[redvett]

Its most likely a front wheel sensor. Can be checked with a Tech 2 have them look at the wheel speeds of both front sensors at the same time while driving.

[GMCTech]

Unfortunately you will need to replace one or both the front wheel bearing/hub assembly(ies).

 

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.

 

Your dealer knows the procedure well to check which wheel speed sensor is the culprit.

 

Hope this helps.