Intermittent Faults

ZB1 Inspect Terminals 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.

If connectors are opened for measurements and checks the terminals should always be inspected visually.

Checks:
- Look for oxidation which may cause poor contact in terminals
- 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 cables lightly and pull on connectors during measurement to locate damage.

ZB2 Open-Circuit:





An open-circuit in a cable will be indicated by the loss of a function (or functions).
Chafed and broken leads are the commonest fault causes.

Checks:
Disconnect connectors at both ends of the cable. Check cable visually according to ZB1.
Connect an ohmmeter between the ends of the cable. The ohmmeter should read approximately 0 if the cable is intact. Shake cables lightly and pull on connectors during measurement to locate damage. If reading is incorrect: Replace cable and/or continue according to ZB6.





- 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.

ZB3 Short-Circuit to Ground:





- A short-circuit between a live cable and ground is often indicated by the loss of a function or a fuse blowing when a current is passed through the cable.

Checks:
- Check cable visually according to ZB1. Activate all switches and sensors in the circuit and check to see if the fuse blows.
- Disconnect connectors in the circuit to ensure that they do not affect readings.

Connect an ohmmeter between cable and ground. The ohmmeter should read infinite resistance if no components are connected. Shake cables lightly and pull on connectors during measurement to locate damage. If the value is not OK, try with a new cable and/or continue according to ZB6.

ZB4 Short-Circuit to Supply Voltage:





A short-circuit between a cable and voltage is often indicated by the loss of a function or a fuse blowing when a current is passed through the cable.

Checks:





- Check cable visually according to ZB1.
- 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 tested and the positions of switches and sensors. Use the wiring diagram to determine the correct voltage in the circuit.

- Use an ohmmeter between suspect cables to detect short-circuits between them. The ohmmeter should read infinite resistance between leads not connected to each other in the circuit. Shake cables lightly and pull on connectors during measurement to locate damage. If reading is incorrect: Replace cable and/or continue according to ZB6.

ZB5 Loose Connections (Terminals):





Loose connections in terminals may be caused by oxidation of the pins and sockets, or by defective connection of a cable to its cable terminal.
Loose connections produce the same faults as an intermittent open-circuit in a cable.

Checks:
- Check terminals visually according to ZB1.
- Continue according to ZB6.

ZB6 Contact Resistance and Oxidation:





The resistance in contacts, cables and terminals should be 0 Ohms. However, a certain degree of resistance will be present due to oxidation of the connections. If the resistance is to great there will be function problems. The magnitude of resistance before it causes a malfunction depends on circuit load. A guideline would be a few ohms.

Cleaning Female Socket Terminals and Male Pin 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 lead.
- Use compressed air to clean the disconnected connector.
- Spray rust solvent spray 1161422 on the disconnected connectors.
- Blow clean with compressed air.

Greasing Terminals:





NOTE: Do not fill the protective cover with grease.

- Press grease, P/N 1161417-9, into female sockets directly from tube.
- Check that cavities are filled in all connectors.
- Use a loose male pin to ensure that contact in sockets is good. The pin should remain in position when pulled gently.