Diesel engine preheating system (Mitsubishi Carisma)

Contents: Checking the diesel engine…⤓ Checking the glow plug relay unit ⤓ Glow plug ⤓

The diesel engine preheating system reduces the time required for starting at low temperatures and makes it almost equal to the very fast starting of petrol engines.

The electronic engine control unit determines the time during which voltage is supplied to the glow plugs after turning the ignition switch to the "ON" position, as well as the glow time of the control lamp for the pre-heating system of the diesel engine, depending on the temperature of the engine coolant.

When the engine control unit detects a malfunction, it sets a fault code corresponding to the malfunction (related to the fuel supply system).

Checking the diesel engine preheating system

1. Check the battery voltage, which should be within 11–13 V.

2. Make sure that the engine coolant temperature is not higher than 40°C.

Fig. 9.40. Measuring the resistance between the wire (1) and the glow plug housing

3. Measure the resistance between the wire and the glow plug body ("ground") as shown in Fig. 9.40.

Note: The resistance value is the resistance of two glow plugs connected in parallel.

The nominal resistance value is 0.3 Ohm.

Fig. 9.41. Measuring the resistance at the glow plug relay connector contacts: "1" - "2" - relay 1 (glow plugs 1 and 3); "1" - "3" - relay 2 (glow plugs 2 and 4)

4. Measure the voltage from relay 1 (glow plugs 1 and 3) and from relay 2 (glow plugs 2 and 4) (Fig. 9.41).

When measuring from the glow plug relay 1 side, connect the ohmmeter to the glow plug wire of the third cylinder and to the body ("ground") of the glow plug of the third cylinder.

When measuring from the glow plug relay 2 side, connect the ohmmeter to the glow plug wire of the fourth cylinder and to the body ("ground") of the glow plug of the fourth cylinder.

5. Measure the voltage immediately after turning on the ignition (without starting the engine).

The nominal voltage value is 9-11 V (the voltage decreases to 0 V within 11-22 s).

6. Also make sure that the glow plug indicator light comes on immediately after the ignition is turned on.

Attention! The current "conduction time" changes depending on the coolant temperature when the ignition is on.

7. Measure the voltage while the starter is cranking the engine crankshaft.

The nominal voltage value is not less than 6 V.

8. Start the engine and measure the voltage while the engine is warming up.

9. The voltage always decreases to 0 V within 10-220 s after the engine starts.

The nominal voltage value is 12-15 V.

Checking the glow plug relay unit

1. Disconnect the glow plug wire and all other connectors from the glow plug relay.

2. Measure the resistance at contacts "1"–"2" and "1"–"3" of the glow plug relay connector (see Fig. 9.41).

The nominal resistance value is 27–35 Ohm.

3. Check the operation of the glow plug relay.

When checking relay 1, connect the "+" of the battery to contact "1" of the connector, and the "-" of the battery to contact "2" of the relay connector.

When checking relay 2, connect the "+" of the battery to contact "1" of the connector, and the "-" of the battery to contact "3" of the relay connector.

Caution: Do not ground the terminals of disconnected connectors.

When using jumpers, be especially careful not to mix up the connected terminals. This will cause the relay to fail.

4. Check for continuity at each terminal when the battery + jumper is connected and disconnected.

When testing relay 1, connect an ohmmeter to contacts "1" and "A" (glow plug wire 3) of the single-pin connector.

When checking relay 2, connect an ohmmeter to terminals "1" and "B" (glow plug wire 4) of the single-pin connector.

When connecting the "+" of the battery, the circuit (conductivity between the contacts) is closed, and when disconnected, the circuit is open.