ABS Problem

[MAKAROV000]

i own an e30 318is since 10 years
recently after driving few km and specially when the car shakes
the ABS light goes on
if i turn off the car and restart it the light goes off
after searching online i did find the ABS sensors tooth
are they the only thing to clean?

[colin86325]

What do you mean "when the car shakes"?  Does you mean that the engine runs rough, or the car is shaking during braking?

If the engine is running rough I'd check the voltage output of your alternator. Low voltage can cause the ABS light to come on.

[MAKAROV000]

The engine is running fine
I mean by shakes is when crossing a pothole

[DesktopDave]

I'd check the ball joints and wheel suspension. The sensor is just a magnet in a little capsule that senses a toothed wheel - if it's coated with rust and road dirt it won't get a good reading from the toothed wheel in the hub. Then you'll get ABS warning lights. BMW does have a way of troubleshooting those, but you can usually get them to work with a good cleaning. Be careful not to stretch or break the sensor wire - it can't easily be repaired. Those sensors are usually a real PITA to get out of the steering knuckle - they tend to get rusted in a bit.

I'd jack the car up securely, then grab the wheel in your hands. Try to shake it side-to-side and then again up-and-down. If the wheel moves any appreciable distance, you'll have to replace some parts. Side-to-side motion is usually a weak idler arm ball joint. Up and down usually means the control arm ball joint is worn. Both usually means a worn wheel bearing.

[MAKAROV000]

till now i removed and cleaned the sensors of the front wheels
the problem is still appearing
still have to clean the back ones
i cleaned the magnetic tooth
should I clean the capsule on which the tooth is installed?
i'm talking about the part on which the tooth sticks on

[colin86325]

Measure the resistance of the sensors.  Typically, one of the front sensors is bad because of the twisting forces it experiences.

[MAKAROV000]

i guess this needs multimeter to do the test
can the sensor be repaired? or should i consider buying a new one?

[DesktopDave]

Sensors are impossible to repair in a practical way, even for professionals - the resistance spec on them is very tight, and some use shielded coaxial wire.

I'd be tempted to repair a known bad sensor unless they're really cheap to buy. What do you have to lose?

[MAKAROV000]

by chance i found the problem
the wire of the front left ABS sensor
few months ago sounds like the mechanic streched the wire while replacing the arm ball joint
i replaced the bad part and all sounds ok till now
thanks all for your replies

[DesktopDave]

No problemo! Glad you got it sorted.

[thedguy]

I fought with ABS problems or a long time.  Every post I ever read always said the same thing "every ABS problem is a sensor (wire) issue"

I even replaced my pump doing an entire rebuild of my brake system... guess what all my sensors had damaged wires.  When I finally got to replace all 4 of them with better ones from the junk yards, my abs started working.