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Re: ANTI LOCK LIGHT Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 22 Oct 2002 12:52:14
In Reply to: ANTI LOCK LIGHT, JonnyT, Tue, 22 Oct 2002 00:25:52 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The ABS constantly runs checks on the ABS sensors. It runs two types of checks - impedance checks, and speed checks.
When the ABS first starts up, it compares the impedance (resistance) of each sensor to the other three. If one sensor is too far out from the others, it sets a fault code and keeps the ABS light on.
The other test is wheel speed. The ABS knows when the brakes are on, and when they aren't. If the brakes are off, it expects all the wheel speeds to be pretty much the same. There is some adjustment to allow for wheel spin on the fronts. But if one sensor isn't sending speed, but the other three are spinning merrily, then it sets a code and lights the ABS light.
There are also other internal self-checks.
Start the car, but don't drive off. Wait for the Brake Fluid light to go out. Wait another 10 seconds or so. If the ABS light hasn't gone out, then it is either a sensor impedance mismatch, or a ABS box internal fault. If the ABS light goes out, but comes back on once you're moving, then it's the speed mismatch.
Either way, the best thing you can do is go to a dealer or independent mechanic with the right tools, and have them read out the ABS codes. This will locate the problem to which wheel, or internal problem if it's internal. Then you can decide what to do. If the impedance is off on one sensor, it could be a bad sensor (replace sensor), worn cable (replace sensor - all one piece) or dirty contacts. They may have gone bad again, it has been two years. If it's speed, it could be a bad sensor, or it could be the toothed wheel mounted on the hub the sensor reads. The wheel could have moved, and sometimes they build up goop between the teeth that interfere with the sensor, especially if you use semi-metallic or metallic pads.
Good luck!
posted by 192.249....
, Tue, 22 Oct 2002 12:52:14 <-- Viewing This Message
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