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Sounds like multiple problems Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 12 Mar 2007 13:48:26
In Reply to: ABS help 1990 SPG, John, Mon, 12 Mar 2007 12:47:56 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The ABS light is on anytime the ABS system detects a problem. The ABS AND Brake Fluid light come on when the ABS pressure is low.
IF earlier you would apply the brakes a few times, the ABS and Brake Fluid lights come on, and the pedal get hard to push, that would be an accumulator problem. 10 hard & fast pushes of the brake pedal to get the lights on is a bit early - closer to 15 would be nice. Make sure that before you run that test, the ABS pump has stopped running. When the lights go out after startup, the pump keeps running for a bit to get the pressure to maximum.
Now, with a 'fixed' accumulator, when you start the car after it had been sitting for a while (like overnight), I'd expect the ABS and Brake Fluid lights to come on. Don't drive anywhere. The Brake fluid light should wink out, indicating that the pressure has reached the minimum (the pump keeps running) and a few seconds later, the ABS light should go out.
If the ABS light doesn't go out, and you haven't driven off, it is likely a ABS sensor problem. The ABS system checks the wheel sensors by comparing the resistance of each sensor to each other. If one is out of whack with the others, the light will stay on, and you'll have no ABS (but the brakes will work). Try cleaning the connectors up by the ABS box, and measure the resistance of the four sensors. They should be each around 1200 ohms. If one is off by 100 ohms or so, that's probably the bad one.
IF the ABS light goes out, but comes back on again when you start moving, then the ABS has determined that one sensor isn't providing the proper signal. It's going to look at the speed pulses from each sensor and if they don't match (and the brakes aren't on), it'll assume one sensor is bad. This can be due to a bad sensor not caught by the resistance check, or a dirty sense wheel. There is a toothed wheel on the hub that the sensor reads magnetically. If gunk gets caught in the wheel, especially metal from worn rotors and semi-metallic brake pads, it can mess up a sensor signal. Cleaning out the gunk can fix the problem.
Or, it's a different sensor. At that point, it takes a special tool to read out the ABS codes.
posted by 192.249....
, Mon, 12 Mar 2007 13:48:26 <-- Viewing This Message
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