PSM

Fault code 0285

Speed sensor, front right

NOTE: This fault can also be caused by a wheel bearing mounted on the wrong side. The multiple-pole ring on the wheel bearing is only integrated on one side. When repairing, always make sure the installation position of the wheel bearing is correct. The correct side (magnetic side) can be determined using a paper clip. --> 4; Rep. Gr. 40, 42; Running gear

Diagnostic conditions
- Ignition on
- Internal PSM control unit function test

Possible cause of fault
- Multiple-pole ring on wheel bearing/speed sensor soiled or damaged (mechanical fault)
- Open circuit in circuit (electrical fault in electric circuit)
- Short circuit to B+ in circuit (electrical fault in electric circuit)
- Short circuit to ground in circuit (electrical fault in electric circuit)
- Incorrect signal/speed sensor faulty/wheel bearing was mounted incorrectly (implausible signal from speed sensor or the magnetic strength of magnetic plates integrated in the multiple-pole ring is significantly reduced)

Affected pins
PSM control unit plug:
- Pin 34 'signal lead'
- Pin 33 'ground'

Diagnosis/troubleshooting PSM 0101

CAUTION: When checking the wheel bearing with multiple-pole ring never use magnetised tools or magnets. This destroys the magnetic plates in the multiple-pole ring.

CAUTION: Resistance measurement destroys the active speed sensor.

NOTE: The PSM control unit supplies '7 mA' of current via signal lead to the active speed sensor when 'ignition is on and during driving'.

NOTE:
Visual inspection: In the next troubleshooting section, please check first that the affected 'pins' on the PSM control unit plug connection and the 'pins' on the speed sensor plug connection are neither damaged nor corroded. Check the speed sensor, multiple-pole ring on the wheel bearing and the front right wire for external damage. Remove any soiling or corrosion/oxidation. Replace damaged parts. Cables '12/13/35' from measurement tool set No. 9684 are needed for measuring the current on the speed sensor.