You just had a noisy wheel bearing replaced, and now your ABS brake light is on, you inspect all the ABS brake sensors, and everything looks ok, none of the sensors or wires are damaged, what could be the problem?
This problem is more common than you would think, and it baffles the DIY guy trying to save a few bucks changing out a wheel bearing on their own.
Here is a possible solution to your problem; the wheel bearing you just installed is in backwards and the encoder is facing the hub, not the ABS sensor!
Here's the Deal on ABS Pickup Rings and Encoders
Old style ABS pickup rings were usually a ring of metal teeth pressed on to the axle, hub, or rotor. These metal teeth are called the pickup, and each one of the teeth are spaced evenly around the ring. There is an ABS sensor mounted at the edge of the ring and it counts or measures the spaces as the ring spins, if any of the teeth are damaged or missing, the ABS brake light will come on warning the driver of a problem.
The new style ABS systems uses a magnetic encoder built into the wheel bearing, and if the wheel bearing is installed backwards with the encoder facing out, it won't take long before your ABS light is on and your stress level goes up. The sad part is, you will most likely have to replace the wheel bearing with a new one, there is only a slim chance you can remove the wheel bearing without damaging it.
ABS Encoders Don't Like Magnets
When handling a wheel bearing with a magnetic encoder, be sure to keep it away from all magnets especially strong magnets like the ones found on speakers. Magnets can damage the encoder ring; even the small pocket screwdriver magnet can cause damage to the encoder ring if it gets too close.
Some car manufacturers make a special tool to check the encoder for damage before installing it; it's worth the extra few minutes to check the encoder before putting everything back together, better to spend a few minutes up front then to see the dreaded ABS brake light on after the job is done. I hate wasting time, because time is money! How bout you?
Old Style ABS Brakes
If you have the old style ABS brakes with the metal ring, it's a possibility you might have damaged the ring when you replace the wheel bearing, or installed the sensor improperly. Also check the sensors for debris build up like road grime or axle grease, sometimes this can interfere with the operation of the ABS sensor. If you find any obstructions, just gently wipe it off with a shop towel and avoid using any harsh chemicals like brake clean or carburetor cleaner, these chemicals could damage the sensor or wires.
Inspect the metal pickup ring very carefully; any damage to the teeth could cause the ABS warning light to come on. Check for missing teeth, broken teeth misalignment and cracks in the pickup ring. If the sensors look good and the rings are in good shape, you may have a bad sensor.
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