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ABS problem solved-EBCM codes not accurate


Bushwack

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http://forums.aaca.org/f116/requesting-help-diagnosing-abs-light-292677.html

For reference, above is a thread I started a few months ago. Finally, was able to solve the problem with this forum's help (thanks to everyone!). Also, I'm writing this post in the hope that should a similar problem arise for someone else, this thread will appear in the search function for ABS and wheel sensor issues.

Briefly, the ABS light on my red '90 vert would come on intermittently; usually after traveling 30..40 feet. The codes I got from the EBCM were 27 (rear outlet valve) and 36 (right front wheel sensor). I pulled the codes numerous times with the same results. My gut told me it wasn't a "rear outlet valve" issue. The ABS light would light up and stay lit after traveling the 30-40 feet without even touching the brake pedal. The light also came on when in reverse. At a cold or warm start up, I could stomp on the brake pedal 20..30 times and the ABS light would stay off.

I tested the ABS a few times driving the car. I took the car up to 20..30..40MPH and hit the brakes hard. Car never came to a skid and would stop straight (at 40MPH, it pulled slightly but not to where it was a concern). Decided to first change out the RF wheel sensor (much less expensive then messing with the Teves).

With a sensor from Jim Finn's Parts Emporium, my mechanic changed the RF wheel sensor. Took the car for a spin but the ABS light stayed on. He then took the sensor and changed the left front wheel sensor (putting back the original right front wheel sensor). ABS light no more! It was the left front wheel sensor (and not the right, as diagnosed by the EBCM code) that was bad. In addition, it seems there never was an issue with the rear outlet valve (took another reading from the EBCM and all is good).

So..if it hasn't been posted yet, it seems the diagnostic codes from the EBCM are not accurate (at least in this regard). I may have been pointed in the right direction but based on the code 27, I was leaning to also change out the rear outlet valve (if I could have located one). Also (and I'm no expert), if the left front sensor, which was bad, would make the ABS inoperable, how come I never came to a screeching stop from 40MPH???

Edited by Bushwack
typo (see edit history)
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