VOLVO Glow Plug System
- Connect 12-volt test lamp across glow plug terminal and ground. Check test lamp and indicator light on instrument panel. See Fig 2.
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- If indicator light is on, but test lamp is out, glow plug relay is defective. If indicator light is out, but test lamp is on, check coolant temperature sender or control unit. If both are out, control unit is defective.
- If both indicator light and test lamp are on, check the amount of time they stay on. Indicator light time should vary with coolant temperature.
- Test lamp should stay on 10-25 seconds longer than indicator. If not enough time is noted, replace temperature sender or control unit.
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- Check operation with starter motor operating. Test lamp should light, indicating voltage at glow plugs. If not check voltage with test lamp at terminal 50 (Blue/Yellow wire) of control unit.
- If there is voltage, control unit is defective. If no voltage, check for open circuit between connector and control unit.
- If test light was on during starter operation, check glow plugs 1 at a time. Place key switch in position "O". Remove bar between glow plug terminals.
- Connect test lamp across battery positive terminal and 1 glow plug. If light is out at 1 or more glow plugs, glow plugs are faulty. If test lamp and indicator fail to light, replace control unit.
- If indicator light and test lamp are both out, check terminal 15 (Blue/Red wire) of control unit for voltage. If no voltage, check for open circuit between fuse box and control unit.
- Check terminal 31 (Black wire) of control unit for voltage (test lamp connected to battery positive terminal and terminal 31). If no voltage, check for faulty ground. If voltage, check for defective control unit.
- If indicator light is on, but test lamp is out, check terminal 86 (Red wire) of glow plug relay for voltage (test lamp connected to battery positive terminal and terminal 86).
- Voltage indicates faulty glow plug relay. No voltage indicates incorrect ground connection. Check terminal G (Blue wire) of control unit for voltage. No voltage indicates faulty control unit.
- Check terminal 30 (Blue wire) of blocking relay for voltage. No voltage indicates open circuit in wire between control unit and blocking relay.
- Check terminal 87 (Red wire) of blocking relay for voltage. Voltage indicates open circuit in wire between blocking relay and glow plug relay.
- Check terminal 86 (Blue/Red wire) of blocking relay for voltage. No voltage indicates open circuit in wire between fuse box and blocking relay.
- Check terminal 85 (Red wire) of blocking relay for voltage (connect test lamp between fuse box positive and terminal 85). No voltage indicates faulty blocking relay.
- Voltage indicates open circuit in wire between blocking relay and instrument panel or defect in instrument panel printed circuit.
- If indicator light is out, but test lamp is on, this usually indicates a failure of either the temperature sender or control unit.
- Disconnect wire at temperature sender. Indicator light should now be on. If so, this indicates circuit from sender to indicator light is okay, but sender is defective.
- Check ground connection at terminal K (Yellow wire) of control unit for voltage (connect test lamp from battery positive terminal to terminal K).
- If voltage is indicated, indicator light on instrument panel is defective, there is a defective wire between control unit and indicator light or printed circuit is faulty.
- If no voltage exists, either the control unit is defective or wire between temperature sender and control unit is grounded.
- If indicator light comes on when engine is warm, disconnect wire at temperature sender and ground it. Turn key switch to driving position "2" and check indicator light.
- If light is on, there is an open circuit in wire between temperature sender and control unit or control unit is defective. If indicator light is out, temperature sender is faulty.