Intermittent Fault
1) Check Connections Visually:
NOTE: When checking the Motronic 4.3 control module, do not remove it from the car until the main relay has cut the voltage supply. This may take up to 150 seconds after the ignition has been switched off.
Whenever the connector is disconnected for inspection or for taking readings, make a visual check of the connector terminals.
- Check for oxidation, which can cause poor contact.
- Check that pins and terminals are undamaged, that they are properly inserted into the connector and that the conductor is properly connected to the pin/terminal. In particular check pins and terminals for the relevant fault.
- Use a loose male pin to ensure that contact in sockets is good. The pin should remain in position when pulled gently.
- Shake cable and pull terminals gently while taking readings to determine where the cable is damaged.
2) Open-Circuit:
An open-circuit in wiring is indicated by a missing function. Worn cables which have come loose are often the cause.
- Disconnect connector at each end of cable.
- Check cable visually in accordance with step 1 above.
- Measure resistance by connecting an ohmmeter between the ends of the cable.
- The ohmmeter should read approx. 0 Ohms if the cable is intact.
Shake cable and pull terminals gently while taking readings to determine where the cable is damaged.
- If the reading is not OK. Replace cable and/or continue in accordance with step 6 below.
Always check control module and control module box connectors to ensure that their pins and sockets are not bent or damaged, this may cause faults. In particular check pins and terminals for the relevant fault.
3) Short-Circuit To Ground:
A short-circuit between a live cable and ground will usually result in failure of the circuit fuse or loss of a function.
- Check cable visually in accordance with step 1 above.
- Operate all switches and sensors in the circuit and check to see if the fuse blows.
- Disconnect circuit component connectors to ensure that they do not affect measurements.
- Use an ohmmeter to take a reading between the cable and ground.
- The ohmmeter should read infinite resistance if there are no components in the circuit.
- Shake cable and pull terminals gently while taking readings to determine where the cable is damaged.
- If the reading is not OK. Replace cable and/or continue in accordance with step 6 below.
4) Short-Circuit to Supply Voltage:
A short-circuit between a cable and voltage will usually result in failure of the circuit fuse or loss of a function.
- Check cable visually in accordance with step 1 above.
- Use a voltmeter to take readings at various points of the circuit while operating switches and sensors.
- The voltmeter reading depends on the circuit being measured and the position of switches and sensors. Use wiring diagram to determine correct voltage in the circuit.
- Use an ohmmeter between suspect cables to detect short-circuits between them.
- The ohmmeter should read infinite resistance when connected between cables which are not connected to each other in the circuit.
- Shake cable and pull terminals gently while taking readings to determine where the cable is damaged.
- If the reading is not OK. Replace cable and/or continue in accordance with step 6 below.
5) Loose Connection (Terminals):
Loose connections in terminals are caused by oxidation on pins and terminals or poor connection of cables. Loose connections result in the same faults as an intermittent open-circuit in a cable.
- Check terminals visually in accordance with step 1 above.
- Continue in accordance with step 6 below.
6) Contact Resistance, Oxidation:
Resistance in contacts, cables and terminals should be 0 Ohms. However, there will be a certain resistance due to oxidation on terminals. If resistance is too great function problems will occur. The magnitude of resistance before it causes function problems depends on circuit load. A few ohms is a guide value.
Cleaning Pins and Terminals:
NOTE: Do not use rust solvent spray or grease on heated oxygen sensor (HO2S) or combined instrument panel connectors.
- Ignition off.
- Disconnect battery negative terminal.
- Use compressed air to clean the disconnected connector.
- Use rust solvent spray 1161422 on the disconnected connectors.
- Blow clean with compressed air.
Greasing Terminals:
NOTE: Do not fill the casing with grease.
- Press grease 1161417-9 into terminals straight from the tube.
- Check that all terminal socket cavities are filled.
- Use a loose male pin to ensure that contact in sockets is good. The pin should remain in position when pulled gently.