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Suggestions Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Sat, 31 May 2008 09:10:22
In Reply to: ABS ISSUE HELP, saabetized, Sat, 31 May 2008 05:00:33 Members see ZERO ads on the bulletin boards and get more feature. - Help Keep This Site Online - Signup |
Because the problem occurs when the car starts moving, the problem is at the sensors, most likely the toothed wheel. The ABS runs two tests - the first is at startup, where it checks the resistance of all of the sensors. Your car is obviously passing this test, because the ABS light is out. The ABS determines the speed of each wheel by counting pulses at each wheel. On each wheel is a toothed gear, and when the teeth go by the sensor, it creates pulses. When you start moving, the ABS compares the speed of each wheel with the others. If one wheel appears to be moving much slower than the others, AND the brakes aren't on, it assumes the sensor is bad and illuminates the ABS light.
This could be a sensor problem - if a sensor is old, it may not be picking up signal as well. Same with a frayed cable - the resistance might not change much and trip the first test, but the signal could be poor. The most likely problem is that there is metallic gunk stuck in the teeth of the toothed gear. With metallic gunk in between the teeth, two teeth appear as one, you get fewer pulses, and the ABS test fails.
Why metallic gunk? Typical road grime and grease gets stuck in the teeth. Metal comes off the rotor with use, and any metal in metallic or semi-metallic brake pads can also get trapped.
A few choices. You can bring the car to a dealer or independent shop and with special tools, they can read out which wheel is the problem. You can jack up and support the car, pull off the tire and clean out the gear. It's on the backside of the rotor, and can be a bit hard to access. Compressed air helps. Wear safety glasses, and all sorts of stuff will fly out.
Or skip the dealer/mechanic, and just clean out the gear teeth on all four wheels. If one is tripping, chances are good at least one other is getting there.
This isn't special to Saabs - any car with ABS is subject to the gear teeth filling up with metallic gunk.
posted by 76.202.162...
, Sat, 31 May 2008 15:03:30, Sat, 31 May 2008 09:10:22 <-- Viewing This Message
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