P0501

VEHICLE SPEED SIGNAL





Fault Symptoms
The CHECK ENGINE lamp (MIL) is on.
The ABS warning lamp may be on.

Conditions.
P0501
^ Engine speed above 2000 rpm.
^ Engine load for more than 3.0 seconds.
^ Vehicle speed slower than 10 km/h for more than 7 seconds.

Diagnostic Help.
A vehicle speed signal can be obtained with the ISAT scan tool.
- Select "READ FUNCTIONS".
- Select "CAR SPEED".

The ISAT scan tool should show the actual wheel speed.

Drive the car and compare the ISAT scan tool's display with the car's speedometer.

Check The Wiring.
Intermittent faults may occur as a result of temporary short circuits and breaks in the wiring. Jiggle the wiring at several points and in different directions to ascertain whether the wiring harness, including any connectors, is causing the trouble. Observe the multimeter, ISAT scan tool or test lamp while doing this.





1. Check the ABS diagnostic trouble codes
- Connect the ISAT Scan Tool.
- Ignition switch in the ON position.
- Select "ABS".
- Obtain readings of the diagnostic trouble codes, if any.

Diagnostic trouble codes for the right-hand front wheel sensor are 44222, 2422B and 24222.

Does the ISAT scan tool show diagnostic trouble code 44222, 2422B or 24222?

YES: Continue fault diagnosis in the Brake System. Then carry out a final check in accordance with point 3.
NO: Continue with point 2.





2. Check the wheel speed signal
- Unplug the control module's 88-pin connector.
- Turn the ignition switch to the ON position.
- Carry out frequency measurement between:
^ Pins 26-79: about 14 Hz.

Is the reading correct?

YES: Continue with point 3.
NO: Check the lead between pin 11 of the ABS control module and pin 79 of the Motronic control module for shorting and continuity. Repair or replace the lead if necessary. If the lead is OK, continue fault diagnosis as described in "Antilock brakes" (ABS Mark IV)





3. Final check
- Clear the diagnostic trouble code.
- Implementation of driving cycle:
^ Drive the car at varying engine loads and rpm for 5 minutes.
- Evaluation of driving cycle:
^ Connect the ISAT Scan Tool.
^ Select "READ FUNCTIONS".
^ Select "CAR SPEED".
^ Check whether the ISAT scan tool shows the same speed as the speedometer.

Does the ISAT scan tool show a different speed?

YES: Continue as described at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: The steps taken to rectify the fault were correct.