Strange ABS Problem

[Geoffzie]

About 7 months ago, I picked up a 1988 BMW 325i convertible with a broken timing belt ... First, a little history on the ABS problem.

I fixed the engine, and have been driving the car for the last few months. But from day one, as soon as the car would begin to roll, the ABS light would come on and stay on. After reading some ABS threads, they said to disconnect all four ABS wheel sensors ... drive the car, and the ABS should NOT light ... it didn't. Then they said to connect ONE wheel sensor at a time ... the wheel sensor that turns the ABS light ON ... is the bad one.

Turned out to be the passenger's (right) rear. Ok, so is it the sensor itself, or the wiring to the sensor?

Since both left and right rear wheel sensors are the same ... I simply switched them ... then ran the above tests again on the rear wheels. If the LEFT rear now lights up the ABS light ... the sensor itself is bad ... if the RIGHT rear STILL lights the ABS light ... the wiring to the right-rear wheels sensor is bad.

Turns out it must be in the wiring somewhere, or the right-rear connection to the ABS pump ... since the right-rear STILL turns the ABS light on.

Fast-forward to the last few of weeks. All of a sudden ... the ABS light stopped coming on! GREAT! the car fixed itself! ... WRONG! Now, the light will sometimes come on when I drive it ... sometimes it will NOT come on when I drive it.

Today, the light did NOT come on ... but the ABS would activate at very low speeds (when speed drops under 10 MPH) when coming to a slow stop. I could feel the peddle pulsating and the buzz of the ABS activating intermittently. The ABS light never came on during any of this.

Any BMW E30 ABS experts out there that might have a clue as to what's going on?

[H.J. 1981]

How are the teeth on the axle? it is where the sensor picks up signals, if there is a lot of rust or debris or anything interfering with the signal input, it may cause an issue. This is a known issue on some BMWs and other cars.

Raise the car, and turn the axle, watch the teeth very closely.

[Geoffzie]

Good thought, next time I'm over at the garage I'll check it out. I could see where an irregularity in what the sensor sees from the axle could "fool" the ABS.

[elder30]

Today, the light did NOT come on ... but the ABS would activate at very low speeds (when speed drops under 10 MPH) when coming to a slow stop. I could feel the peddle pulsating and the buzz of the ABS activating intermittently. The ABS light never came on during any of this.

Any BMW E30 ABS experts out there that might have a clue as to what's going on?

Any resolution on this? I have the same issue -- though the light is intermittent.

[richardodn]

Start here https://www.bimmerforums.com/forum/s...9#post28744779