ABS sensor hell

[joako]

I already replaced the front ABS sensors months ago, no issues.

Now I tackle the front ABS sensors and I can't get it working right.

The original problem for all 4 sensors is the cables are frayed and the insulation is pealing off, when I drive through puddles the ABS light goes off, etc. Very simple problem and solution.

I changed the rear ABS sensors and the speedometer didn't work, ABS activates every time I hit the brakes. I got 2 more sensors and now my speedometer reads FAST and also my ABS engages every time I brake, until the ABS and DSC lights turn on.

What the hell is going on?

[rf900rkw]

Hook up your INPA and watch the wheel speed data for all four corners. It doesn't take any fancy or dangerous stuff.... just roll across an empty parkinglot. Watch for dropouts and/or flakiness.

[joako]

When I connect the OBD cable to the port inside the cabin I can't communicate with the ABS... my car is 1998.

But I have removed the wheels and jacked up the rear, both sides constantly read something but they aren't the same.

But like I said I had 2 original sensors, I replaced those and then I got another 2 more sensors and that still has issues, albeit the opposite.

[rf900rkw]

I have the adapter, if you're near the northeast corner of the southeast. :)

Air gap, or crap in the tone wheel teeth are my two guesses. My nominal test for airgap is to stick a piece of cardboard to the end of the sensor with a dab of grease, insert, turn the wheel, and see if there is contact. I don't know if BMW publishes a spec... but generic auto mag sensor airgap is in the .030" area.

[joako]

The breakout box for the ABS module connector?

What do you mean by airgap? I would have to change the hubs if that's the case?

--- Also the ABS and DME will exit diagnostics mode when the "vehicle speed" exceeds ~10mph!

[rf900rkw]

I was talking the 20pin. I guess you meant you couldn't use the 20pin and drive. I use a USB extension cable for that. And yes, the system kicks out at 20 kph. Annoying, but good enough for a beginning signal test.

Airgap as in distance from sensor tip to the tone wheel. I was thinking more of variations in sensor length. some people have complained about aftermarket sensors being flaky. I've also seen loose wheel bearings cause issues.

[joako]

Ok I figured out if I unclip the OBD plug under the hood I can close the hood with it connected and the cable reaches a laptop in the passenger seat. The right side sensor reads slower and the other 3 read the same speed.

It seems like the car was reading faster speed that it was traveling.. so I was thinking maybe the left side sensor is bad. Now to try the 3 senors I have here and figure something out.

Thanks for getting me to do this with all 4 wheels on the ground, comparing 2 speeds is harder than 4!

Ok I just went through 3 sensors on the same wheel and it always reads really low. I had already sprayed brake parts cleaner in the hole to try to clean it out. So this means I need a new hub? or how do I fix this?