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Re: Another Anti-lock light Q ****update !!***** Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 11 Jul 2005 06:12:34
In Reply to: Another Anti-lock light Q ****update !!*****, JeffR [Profile/Gallery]
, Sat, 9 Jul 2005 16:48:51
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The anti-lock system is continuously running self-tests. When the car is moving, the system compares the speed signal from all four wheels, and expects them to be the same if the brakes aren't applied. If they are different, it'll light the ABS light, and it'll stay ON until the car is shut off.
If the signal from one sensor is just a little weak, sometimes it'll trip the threshold, other times it won't. This can be due to a tired sensor, a break/crimp in the signal wire, a bad connection in the sensor to ABS box, or metallic gunk building up in the toothed wheel on the hub. Or a combination. It's sitting on the hairy edge of hitting the 'turn on the light' threshold - sometimes it goes, sometimes it doesn't. So most things you do will have no correlation - you could add brake fluid and the light goes out. But if you had bran flakes for breakfast, the light may stay out, too.
If you can get it to fail, and bring it to a shop, they can read out the ABS code with a code reader. That should point to the weak sensor. Alternatively, you can re-seat all the ABS connectors at the ABS box, inspect the ABS sensor cables for wear (usually in the wheel-well), and pull the disks and clean out the ABS gear teeth. The ABS sensor is just a coil of wire, and on the hub there is a toothed gear. As the teeth go by, they induce a very small voltage into the sensor. The teeth produce electrical pulses, and the ABS system counts the pulses to determine wheel speed. If there is metalic gunk in between the teeth, the count will be off, and the wheel will look like it is turning slower.
As to how the brakes feel, unless you lock up a wheel, no ABS feels just like ABS. There is no change to normal braking, or even very hard braking. Only in cases where you would lock up a wheel will it feel different with the ABS light ON - the wheel will skid.
posted by 192.249....
, Sat, 9 Jul 2005 16:48:51, Mon, 11 Jul 2005 06:12:34 <-- Viewing This Message, Mon, 11 Jul 2005 21:12:03
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