Power and Ground Distribution: Service and Repair

CHECKING LEADS AND CONNECTIONS:

CAUTION: When checking a control module, do not remove it from the car until the main relay has cut the supply. This can take up to 60 seconds after the ignition is switched off.

Faults in electrical systems are often due to faulty leads and poor connections. These faults are mainly the result of interference from other electrical systems and mechanical or chemical effects. For repairs to leads and connectors, use Volvo spares kit 914 8210, which comes with repair instructions and special tools.

Checking Connections Visually:





Check leads visually when making any tests or checks which involve taking connectors apart.
- Check for signs of oxidation which could affect contacts in connectors.
- Check that male pins are undamaged and that copper leads are properly connected to pins.

Open Circuits:





Open-circuits in leads show up when something does not work. Rubbed, worn or loose leads are the usual causes of this.
- Undo connectors at both ends of lead.
- Using an ohmmeter, measure across the ends of the lead(s). Ohmmeter should read approx. 0 ohm if there is no open-circuit in a lead.

Checking intermittent open-circuit:
- Check lead(s) visually as instructed above.
- Shake lead(s) and pull connectors gently while testing to see where lead is damaged.

Short Circuit To Ground:





A short-circuit between a supply lead and ground usually shows up when a fuse blows when switching power on or something does not work.
- Operate all switches and sensors in a circuit and see if fuse blows.
- Undo connectors from components in circuit so they do not affect tests.
- Using an ohmmeter, measure between lead and ground. Ohmmeter should read infinite resistance with no components connected.





Checking intermittent short-circuit to ground:
- Check lead visually as instructed above.
- Shake lead and pull connectors gently while testing to see where lead is damaged.

Short Circuit To Supply:





A short-circuit between a lead and supply usually shows up when a fuse blows when switching power on to that lead or something does not work.
- Take voltmeter readings at different points in the circuit while operating switches and sensors. The voltage reading will depend on the circuit involved and the positions of switches and sensors. Use circuit diagrams to find the correct voltage for a given circuit.
- Take ohmmeter readings between leads where you suspect there is a short-circuit between them. Ohmmeter should read infinite resistance between leads which are not connected to one another in circuit.





Checking intermittent short-circuit to supply:
- Check lead visually as instructed above.
- Shake lead and pull connections gently to see where lead is damaged.

Loose Contact (Connections):





Loose contacts in connections are caused by oxidation in pins and contacts or leads not connected properly. Loose contacts have the same effect as intermittent open-circuits in a lead.
- Check lead visually as instructed above.
- Shake lead and pull on connections gently to see where lead is damaged.





- Always check control module and control module box connectors for bent or damaged pins or sockets, this may be where the fault is.

Contact Resistance and Oxidation:
Resistance in contacts, leads and connections should be 0 ohm. There is always some resistance due to oxidation on contacts, however, if resistance becomes too high, things may not work properly. How high the resistance can be before problems occur depends on how large the load is in the circuit. This is normally a few ohms. Check connections visually as instructed above.

Cleaning contacts and male pins:





CAUTION: Do not use rust removal spray or grease on any HO2S (Oxygen sensor) connectors. Also, lubricants or sealants containing silicone may permanently damage oxygen sensor(s).

- Turn ignition off.
- Disconnect battery negative terminal.
- Spray rust removal spray (part no. 116 1034-2) on the connector once undone.
- Blow clean with compressed air.