testing wheel speed sensors.

[mcbonio]

Ok so having a few ABS problems, the ABS light goes out after engine start and then comes back on when in motion. Which means wheel speed sensor fault.!

How can I single out the bad sensor?

[PG325]

Test the wiring at the ABS ECU.

[mcbonio]

Are the front ABS sensors interchangeable? Or is that the rears?

Anyone know? Brian?

[mcbonio]

Bump

[daimlerman]

Front sensors are handed.

Check each sensor for resistance,the one with the 'odd' reading is your culprit.

[Speedtouch]

"To check the resistance of the sensors, unplug the white connectors just before the wire goes through the front wheel arches and check the resistance is about 1 kilohm with a multimeter. The rear ones are under the back seat."

http://www.e30zone.net/e30zonewiki/index.php/ABS

[stew72]

Front sensors are handed.

Check each sensor for resistance,the one with the 'odd' reading is your culprit.

this but the odd one will be a problem if two have failed A working sensor will vary in resistance when the hub is rotated, a failed one will indicate an open circuit.

If all looks ok with the sensors be sure to check all earths and live feeds before blaming the ecu.

[mcbonio]

A bad sensor will still pass a resistance test.


I found a great thread on another site dedicated to testing the ABS system on an e30. I'll find it and post it. It's basically this;

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If the ABS light comes on and stays on when the car is started, its an ECU, pump or relay problem.

If it goes out upon starting then comes back on when the car is in motion, its a sensor problem.

A good way of testing sensors is to unplug all but one, and go for a drive, it the ABS light comes on then that sensor is good and working. The ABS light comes on as the ABS ECU knows the car is in motion and there are sensors missing. If the ABS light stays off then the sensor is bad as the ABS computer doesn't know the car is in motion, indicating a bad sensor.

Test each one at a time like this.

[stew72]

A bad sensor will still pass a resistance test.


I found a great thread on another site dedicated to testing the ABS system on an e30. I'll find it and post it. It's basically this;

-----------

If the ABS light comes on and stays on when the car is started, its an ECU, pump or relay problem.

If it goes out upon starting then comes back on when the car is in motion, its a sensor problem.

A good way of testing sensors is to unplug all but one, and go for a drive, it the ABS light comes on then that sensor is good and working. The ABS light comes on as the ABS ECU knows the car is in motion and there are sensors missing. If the ABS light stays off then the sensor is bad as the ABS computer doesn't know the car is in motion, indicating a bad sensor.

Test each one at a time like this.

It's a good place to start. What type of sennsors are fitted to E30's? Normally cars of this age have magnetic sensors so dirt and damage to the trigger rings can also give the same symptoms as this test. In my experience a failed sensor has no continuity.

[capnmchl]

For inductive sensors, unplugging and using an AC voltage test and spinning the wheel rather than an ohms test is a preferable method. Or do both.

[Brianmoooore]

A simple resistance test will show up most duff sensors, but occasionally there'll be one that has the right resistance but is still dud.
Easiest way to check is to connect an AC voltmeter to the pairs of pins of each sensor in the (unplugged) ABS ECU plug in turn, while driving the car a short distance.

[mcbonio]

Yeah the duff sensor mine has passes a resistance test fine, but when I drive with just that sensor plugged in the ABS light stays off as the ABS ECU thinks the car is stationary. Therefore that sensor is fooked where as if it were working the ABS would throw a light as it knows the car is moving and realizes there are sensors missing - indicating a working sensor.

Its a long winded but surefire way of testing them.

[Brianmoooore]

Yeah the duff sensor mine has passes a resistance test fine, but when I drive with just that sensor plugged in the ABS light stays off as the ABS ECU thinks the car is stationary. Therefore that sensor is fooked where as if it were working the ABS would throw a light as it knows the car is moving and realizes there are sensors missing.!

Nice bit of lateral thinking! If the sensor was giving an output below whatever voltage threshold the ECU needs, then this would work.

[mcbonio]

Its how I ratted out my faulty sensors.