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ABS Light

(1990 Mercedes-Benz 420SEL)
in Santa Maria, CA on May 04, 2010
My ABS Light stays on all the time and my brakes have been changed. Why does the light stay on?
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Popular Answer
on August 08, 2010
Had same problem after a front brake job. This answer will apply to vehicles with Magnetic Wheel Sensors; Of course, always check the easy stuff first like connections, brake fluid level, etc. The best thing to do is get access to an ABS Code reader (this code reader is different than your standard code reader, and repair shops will charge you about $50 and up (only takes a few seconds) to give you a diagnosis from their Code Reader. It is pretty accurate and pinpoints the problem most of the time. Most auto parts stores don't loan ABS code readers out like they do the standard code readers. Since I didn’t want to spend the money for the service, I used the internet for information and talked to several "brake experts." Consensus seemed to point to a defective wheel sensor. Maybe yours was damaged during the brake job. But this was not the case for me. My story: After jacking up the car and removing the caliper, I removed the whole rotor assembly, both the hub and rotor. The hub has to be removed from the rotor so just the rotor can be taken in for resurfacing. In the process of removing the hub, a wheel seal has to be removed so that the bearings can be removed. In the process of removing the wheel seal off the hub (to get the bearings out), I used a screw driver to pry out this (wheel) seal. Doing so bends and damages the seal. In most cars this is o.k., as it can be reinserted after straightening and smoothing it out. BUT NOT IN VEHICLES WITH MAGNETIC WHEEL SENSORS WITH TONE RINGS IN SEALS! My front wheel seals happen to have a "Tone Ring," a small thin metal band around and inside the seal. This is what the magnetic wheel senor uses to read the speed. I damaged the seals and tone rings when I pried them out. It only cost me $7 a seal to replace. For 14 bucks that took care of it. I spent $100 on wheel sensors it didn’t even need. So if your vehicle happens to have magnetic wheel sensors, and if the rotors were removed for resurfacing, chances are the wheel seals may have been removed and caused damage to the tone rings. Other suggestions I tried that failed were: Disconnecting battery for 30 min. so it could reset, stepping on the brake & turning the steering to the left and right etc for resetting. After I replaced the new seals, I had to drive the vehicle a few hundred yards and apply the brakes a couple of times for the ABS/ESP/BAS lights to FINALLY turn off.
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on May 04, 2010
Because ther is a fault in the ABS System. You'll need to have the ABS System inspected and diagnosed to know why the light is on.
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on June 12, 2010
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