2000 Blazer LS 160k. New owner.

When I started the truck before the following event, the ABS system light came on then went off. Shortly after this I used the brakes and they felt like a rotor had warped - fast pulsing feedback on the brake pedal on a high-speed slow-down at an interstate exit ramp. I figured that this is a symptom of the ABS system "pulsing" the brakesin a near-wheel-lockup situation. Oddly, this was not the case! The braking was occuring on dry pavement under normal,non-emergencystopping conditions.I do not believe that the wheels were anywhere close to locking. This was also my second drive at interstate speed. The first came earlier that day.

This is may first ABS-equipped vehicle and my knowledge about ABS is basic.

What would be a good starting point for diagnosis?

 

Is it actually pulsating in the pedal or is it just shaking. If its pulsating it is most likely an ABS sensors on the wheel.

 

Hello, My name is Jim and I am a NOOB.

(chorus: "Hello Jim!")

I admit it, I didn't use search, I didn't ask anybody locally. I just posted.

(chorus: "It's okay, jim. Admitting that you are a NOOB is the first step on the journey to happiness with your Second Generation Blazer!")


...Okay, I understand that there is a a braking threshold that, when reached, causes the ABS system to take over when you mash your foot down on the Stop Pedal.

I have things to get used to with this truck. It's nothing like the Samurai, Tracker, Sidekick or older Rangers that I have owned. Right now I am trying to keep track of the truck's corners.They are so far away - ina relative sense

 

The only reason for the ABS system to 'take over' braking is when it detects a difference in the wheel speeds as reported by the wheel speed sensors (one at each front wheel and the VSS -vehicle speed sensor for the rear axle as a whole).

I'll reiterate port's question that you did not answer. Are you sure that this was the ABS system activating?

And the sensors don't typically just go bad. They can sometimes get dirty due to brake dust getting into the reluctor ring (square toothed ring that the ABS sensor uses to determine the wheel speed), masking the notches in the ring, causing the ECBM (electronic brake control module) to lose its signal. Another possibility is a pinched or otherwise exposed wire that may be grounding out, causing the system to activate.

I would recommend that you pull the front wheels and inspect the wiring for the ABS speed sensors. If you find no problems with the wiring, then you may have to pull off the brake calipers, caliper brackets, and rotors to get to the speed sensor. (TIP: do not allow the caliper to hang by the brake hose). Remove the speed sensor and have a look at the ring inside. If it has junk in the notches, clean it out (vacuum cleaner with a small nozzle on the end and a small screw driver works well).

 

To answer this question, it felt like rapid pulsing - like one of the front rotors was warped or wobbling due to a bad wheel bearing (Samurai experiences). Unlike a warped rotor or bad wheel bearing, the "problem" went away the next time I used the brakes.

My take on the incident was that I had my first experience with ABS braking. Really!

When I have some time (next winter or if the symptom appears under light braking - whichever comes first), I'll tear down a front wheel assembly and check out the ABS sensor system.

Thanks for the help!

 

Update:

Okay, I guess it wasn't the ABS afterall. I drove it this weekend on my "other job" and discovered that there was a shaking sensation in the pedal and ever-so-slightly in the vehicle itself whenever I applied the brakes. Otherwise it rolls smoothly, steers crisply and tracks straight.

Is this a common symtom of something?