Checking Wiring and Connections

Checking wiring and connections. Permanent faults





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.

Checks:
- Check for oxidation, which can cause poor contact. Check that that pins or sockets are not damaged, that they are properly inserted into the connector and that the conductor is properly connected to the cable pin/socket. Check in particular the pins and sockets for the relevant fault.
- Test with a separate male pin to see if the female socket provides adequate contact. Check also that it is properly attached by pulling lightly on the male pin.









Open-circuit
An open-circuit on a cable can be indicated by loss of a function or functions. Worn cables or terminals which have come loose are common causes of faults.

Checks:
- Disconnect connector at each end of cable.
- Measure resistance by connecting an ohmmeter to each end.
- The ohmmeter should read approx. 0 ohm if the cable is intact.
- Always check control module and control module box connectors for bent or damaged pins or sockets, these can cause faults.
- In particular check pins and sockets for the relevant fault.

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 (or functions).

Checks:
- 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 measure resistance between the cable and ground.
- The ohmmeter should read infinite resistance if no components are in circuit.
- Check in particular pins and sockets for the relevant fault.

Short-circuit to supply









A short-circuit between a cable and the supply will usually cause the circuit fuse to fail when the cable becomes live or may cause the loss of a function (or functions).

Checks:
- Use a voltmeter to take readings at various points of the circuit while operating switches and sensors.
- Voltage indicated by instrument will depend on particular circuit and status of switches and sensors. Use wiring diagram to determine correct voltage in the circuit.
- To locate short-circuits, use ohmmeter to measure resistance between suspect cables.
- The ohmmeter should read infinite resistance when connected between cables which are not connected to each other in the circuit.
- Check in particular pins and sockets for the relevant fault.









Contact resistance, oxidation
In theory, the resistance across contacts, leads and terminals should be 0 ohm. However a certain resistance is always present due to oxidation on terminals.

If contact resistance becomes excessive problems with functions will occur. The value which is tolerable without impairment of the function is dependent on the circuit load. A typical value is a few ohms.

Checks:
- Check cables visually.

Cleaning male pins and female sockets

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 detached connector.
- Spray connector halves with rust solvent, P/N 1161422 (1161435 USA/CDN).
- Blow clean with compressed air.

Greasing female sockets









NOTE: Do not fill the casing with grease.
- Pack connector halves with grease, P/N 1161417-9, directly from 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.





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.

Checks:
- 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.









Open-circuit
An open-circuit in wiring is indicated by a missing function.
Worn cables which have come loose are often a common cause.

Checks:
- Disconnect connector at each end of cable.
- Check cable visually.
- Measure resistance by connecting an ohmmeter between the ends of the cable.
- The ohmmeter should read approx. 0 ohm 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 Contact resistance, oxidation.

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.

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.

Checks:
- Check cable visually.
- 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 Contact resistance, oxidation.

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.

Checks:
- Check cable visually. 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 Contact resistance, oxidation.





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.

Checks:
- Check terminals visually.
- Continue in accordance with Contact resistance, oxidation.









Contact resistance, oxidation
Resistance in contacts, cables and terminals should be 0 ohm. 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.