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Speed signal

Symptom: Somewhat poorer idle air control when driving in stop-and-go traffic.

Speed signal



Fault symptom

Somewhat poorer idle air control when driving in stop-and-go traffic.



Diagnostic procedure


1. Connect the ISAT and activate the command "WHEEL SPEED RF" in the "READ FUNCTIONS" menu. Drive the car and compare the speed shown on the ISAT\`s display with that of the car speedometer.

If the speeds coincide, turn to for further diagnostic instructions.

If the speeds do not coincide, continue with the next point.

2. With the ignition switched off, connect a BOB to the MOTRONIC control module and cable.


Raise the car, turn the ignition switch to the Drive position and rotate the right-hand front wheel. The voltage measured across pins 9 and 14 should now change between 0 and 10 V.

If it does not, continue as described below.

3. Check the lead between pin 9 of the MOTRONIC control module and pin 7 of the ABS control module for continuity/shorting.

If the lead is OK, check the output signal from pin 7 of the ABS control module. See ABS fault diagnosis in Service Manual 5 "Brakes".