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Re: ABS/TCS control lights on the dashboard '93 9000 Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 12 Apr 2007 13:42:04
In Reply to: ABS/TCS control lights on the dashboard '93 9000, Ryan Davidson, Thu, 12 Apr 2007 07:10:36 Members do not see ads below this line. - Help Keep This Site Online - Signup |
If the ABS senses a fault, it will drive the ABS light. Since the TCS uses the ABS for some inputs (such as wheel speed), the TCS also turns itself off and lights the TCS light. So chances are it is an ABS problem.
When you first start the car, it is typical for the ABS and Brake Fluid lights to come on for a few seconds. Then the Brake Fluid light goes out, followed by the ABS light. Or it should. So - does the ABS light go out, and then come on when you drive off, or does it come on and stay on?
The ABS does a few self-tests, but two concern the wheel sensors. The light stays on until it completes the first test. In the first test, it measures the resistance of each of the four wheel sensors. If one (or more) is out of range, it keeps the ABS light on. This is the test it runs when the car is motionless. If the wheel sensor resistances are OK, the light will go out.
Once the car starts rolling, and assuming it passed the resistance test (light out), the ABS compares the wheel speed signals from all four wheels. It knows if the brakes are on, so if the brakes are off, all the wheels should be going the same speed. If one isn't, it lights the light. This would be the case if the ABS light goes out, but comes back on once you start moving.
There are other tests, but this covers a lot.
If you've failed the resistance test (light stays on while the car is motionless after start), check the sensor resistance. The ABS box is under the cover at the base of the windshield (open the hood, remove horizontal cover, on the driver's side US cars). The four ABS cables come up to funny connectors that look like short, black pencils with a wire out each end. First, pull apart and then reseat each connector. That itself might just fix it (this cleans the connection slightly). If not, take an ohmmeter and measure each sensor side. It should be one the order of 1200 ohms, +/- 200 ohms (I think). If one is way out - like an open circuit - you need to replace that sensor.
If the problem occurs only after the car starts moving, then it is likely that there is a buildup of metallic material in the shutter wheel the sensor looks at. This is a gear-like wheel on the hub the ABS sensor looks at. If the teeth fill up with gunk (like dirt, grease, and metallic bits worn off the rotor and some semi-metallic brake pads), it can mis-count teeth. If that's the case, clean out the teeth.
If that doesn't do it, bring it to a dealer or Saab Indy and have them read out the codes.
posted by 192.249....
, Thu, 12 Apr 2007 13:42:04 <-- Viewing This Message, Sat, 14 Apr 2007 06:17:19
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