ABS sensors testing procedure

[shogun]

pertains to a E32 , build year. 08/1988 ,730i
(could also work for other models)


The sensors are quite easy to test with a simple ohm meter, Remove the cover from the motronic enclosure (4 screws), situated on the passenger side (left hand drive car) in front of the windshield. The ABS mudule is closest to the cooling fan, The brown relay between the modules is the ABS relay. Unlock the plug from the ABS module and pull it off

You cannot measure to ground because both conductors, center and shield, run directly to the connector on the ABS controller and are connected to ground through the controller. If you pull the connector, you disconnect the ground.

This is how one does it:

Pull the connector off the ABS module and turn it upside down. You will see 2 rows of pins, a short row and a somewhat longer row. The shorter row contains the odd numbered pins, the longer row contains the even numbered pins. The counting starts from the side opposite the cable entry, so from the fender.

now measure simply on the following pins:

Pin 4 and 6 = sensor left front 1000 ohm (red center)
pin 9 and 7 = sensor left rear 1000 ohm (white center)
pin 21 and 11 = Sensor right front 1000 ohm (yellow center)
pin 26 and 24 = sensor right rear 1000 ohm (green center)

where 4, 9, 21 , 26 are the shields=ground. transparent insulation.

one can open the plug easy by loosening the 3 screws. One can check if the colors are correct and see the numbers on the pins.

The resistance values can vary between 600 and 1600 ohm. Values below mean there is a short in the cable or sensor. The sensors have a 2 pin connector to feed through the frame. One in each front wheel well. The rear ones are probably under the rear seat.

You can measure directly on the plug but measuring on the ABS module is probably easier.

Most likely the cables in the wheel wells are broken because of the constant movements.

here you will have to remove the sensor and measure.

[Ross]

Thanks for the spec on the sensors. Do you know if E39 sensors should test the same?
I'm currently diagnosing intermittant ABS/DSC failure on an E39 and the $100 Bentley has zero info on the system.

[shogun]

Have no idea for E39, these data are from a friend in Germany who tested it.
Maybe you just measure them and see what the result is.

[Ross]

Will do. From what you have given me regarding E34 I think it's safe to assume they should all be the same. It's someplace to start.