"ABS Active" light
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,261
Likes: 4
From: Middle River MD
"ABS Active" light
The ABS active light has been coming on in my '89 at strange times lately, and I can hear the pump running as well. It should only do it upon initial movement after startup. It will do it while stopped at a light then go off if I creep forward. Whats going on...thanks.
Pro
Joined: Mar 2007
Posts: 595
Likes: 355
From: Mt Prospect IL
2025 C4 of the Year Finalist - Unmodified
You may have a bad wheel speed sensor that gives a false reading when going very slow. Check the ac voltage output from each sensor at low speeds and see if there is one that is acting erratic (jack up vehicle and spin tire by hand about 1 revolutions per second). It could just be dirty or it may need replacing.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
There should be a sensor/pick-up on each of the 4 wheels. Remove the wheels from the car one at a time and you'll find a wire that goes directly to each hub area. At the end of the wire there is a sensor attached. Remove the retaining bolt that holds the sensor in place and pull the sensor straight out of the hub. Do not flex the wire too much as the insulation on it may be brittle from age and exposure. Clean the sensor tip (looks like a flat bladed screwdrive tip) remove any debris of shavings that may be stuck to it. Then reinstall it. If your handy with a voltmeter you can check the resistance to the sensor by finding the plug end of the sensor wire and check the resistances reading while slowly spinning the wheel. Depending on the tooth postion of the spindle in relation to the pick-up sensor's tip the resistance should be between ~900 and ~1,200 ohms...if you spin the wheels you should be able to see is cycle between the 2 ranges.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,261
Likes: 4
From: Middle River MD
There should be a sensor/pick-up on each of the 4 wheels. Remove the wheels from the car one at a time and you'll find a wire that goes directly to each hub area. At the end of the wire there is a sensor attached. Remove the retaining bolt that holds the sensor in place and pull the sensor straight out of the hub. Do not flex the wire too much as the insulation on it may be brittle from age and exposure. Clean the sensor tip (looks like a flat bladed screwdrive tip) remove any debris of shavings that may be stuck to it. Then reinstall it. If your handy with a voltmeter you can check the resistance to the sensor by finding the plug end of the sensor wire and check the resistances reading while slowly spinning the wheel. Depending on the tooth postion of the spindle in relation to the pick-up sensor's tip the resistance should be between ~900 and ~1,200 ohms...if you spin the wheels you should be able to see is cycle between the 2 ranges.
Instructor
Joined: Aug 2005
Posts: 206
Likes: 1
From: Milwaukee WI
If a wheel bearing is going bad you may have metal shavings where the sensor is trying to pick up the signal on the rotor inside the bearing assembly. This would screw up the signal. Jack up the car and wiggle the wheels to test.
Jeff
Jeff
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Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,261
Likes: 4
From: Middle River MD
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Well I believe you solved the mystery. That wire was not "clicked" in very tight. Plugged it in tight and the symptom did not repeat. I was checking the vacuum line to the booster recently and must have inadvertently pulled it loose....hope this proves to be the cause, so far looking good
