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  #1  
Old 12-06-2010, 09:14 AM
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Default ABS Activation at Low Speeds

Since I'm on here often enough looking for help, I figured I would post my issue and solution:

At low speeds while braking, the ABS would activate making the characteristic grinding sound as the vehicle came to a stop.

Using the GM Tech II device, I was able to determine that the right front wheel speed sensor was reading 3 mph while the other sensors were reading 5 mph as the vehicle slowed. 3 mph being the zero value for the wheel speed. When this happened, the ABS would engage. Without a Tech II, you would likely have to spin the wheel and read the output with a multi-meter.

Once I had identified the issue was with the front right sensor, I first tried to execute the TSB posted on this sight, and thoroughly clean the mounting surfaces. This didnít work.

While cleaning the surface however, I had noticed that the mounted sensor had 3 shims tack welded in between the sensor and hub. Since I had almost given up and was ready to replace the hub, I chiseled off one of the shims, which resulted in closing the gap sufficiently between the sensor and reluctor wheel inside the hub, remedying the issue of the ABS activation at low speeds.
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Old 12-06-2010, 11:16 AM
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When I had this problem a year or so ago it tuned out I had play in a front hub bearing which was upsetting the air gap between the reluctor wheel & sensor. A new hub assembly cured that. Whats more, the new hub came with a new ABS sensor so I took the old sensor out of the old hub to keep as a spare.
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Old 12-06-2010, 12:54 PM
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Hub was relativly new. Say 2 years old versus the other side which has 170k on it. I was hoping not to replace the hub since it was basically new, and had no play in the bearings.

We'll see how long this lasts, and thanks for the tip.
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Old 12-06-2010, 01:06 PM
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Clay--
I had a similar problem with ABS going on at low speeds accompanied by a grinding noise. I had my breaks and rotors replaced. So now the grinding noise is gone, but my ABS light remains on constantly. When I tested the code, it said that my driver side wheel speed sensor wasn't sending information and was stuck open, and that my passenger side wheel speed sensor was stuck open. Have you experienced this at all? Is it possible that BOTH of my speed sensors went bad. Or do I need to be checking into replacing my EBCM?

Thanks!
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Old 12-06-2010, 02:34 PM
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You need to start checking, but I wouldn't look at replacing the EBCM until you at least verify that the wiring is intact and that the sensors are actually reading properly.
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Old 12-06-2010, 10:52 PM
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I checked all of the wiring and it checked out just fine. I forgot to mention that in my previous post.. How else can i check to make sure the sensors are reading properly?
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Old 12-07-2010, 03:47 PM
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Clay- Does your problem sometimes come with a sudden thud or clunk sound when coming to a stop? My brakes have been acting up lately and at times lock up and keep me from accelerating. Any way to disconnect ABS to see if this is the problem?
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Old 12-08-2010, 12:00 PM
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Isaimendez4:
Pull the fuse on the ABS under the hood to "turn off" the ABS system. The ABS light should light on the dash once the vehicle moves. If the problem is gone - It's likley in the ABS. On mine it's a large 60 amp fuse.

waviaerith:
No signal from either sensor? My '98 has three sensors - although I have not bothered to locate the third for the rear wheels.

Most likley the grinding noise was the ABS activating. You would have to be the judge of exactly what the grinding noise was. The fact that the ABS light is now on, and the noise is gone makes me think the ABS is no longer operating, hence the grinding noise is now gone.

Start checking the wiring to the wheel sensors. If the wiring appears ok, I would start digging on how to check a sensor. I think the sensor outputs a voltage based on the speed of the reluctor wheel if I remember the service manual correctly. Two open sensors makes me think the brake shop removed them and put them back in an effort to fix your problem, and now they are both out of wack.

I have limited time and only a few special tools, so if the job looks like trouble, I either spend time hunting how to solve the problem or let a shop handle it. Any job thats more then a few hours I dont like to do, unless it's summer and I have time to kill.

Last edited by Clay_Assassin; 12-08-2010 at 12:08 PM.
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Old 12-12-2010, 08:04 PM
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Default abs check

to check the wheel speed sensors us a multimeter set at ac volts and probe the harness at the end of the wheel sensor. you can unplug it if it helps. once your meter is connected spin the wheel with your hand, the voltage reading should increase the faster you spin the wheel. if you cant get a reading check the ohms to see if you resistence you should not have an open or OL. thats probably a bad sensor. if the sensor is okay check the bearing assembly. and i forgot to mention, the wires and harness that lead to the EBCM those can also cause faulty readings. the rear wheel sensor is the same as the vehiclle speed sensor located on the transmission output end it is the one with two wires
Old 12-12-2010, 08:04 PM
 
 
 
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abs, activates, activation, blazer, chevrolet, chevy, disconnect, low, reluctor, sensor, shim, speed, speeds, stop, wheel


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