Inspection Procedure 4

Engine Coolant Temperature Gauge does not Work.






CIRCUIT OPERATION
- The ignition switch (IG1) circuit is the power source for the engine coolant temperature gauge.
- Resistance value, which the engine coolant temperature gauge unit sends to the combination meter, is dependent on temperature of the engine coolant. This causes circuit current to fluctuate.
- The engine coolant temperature gauge moves the needle according to the circuit current.

TECHNICAL DESCRIPTION (COMMENT)
If the ignition switch (IG1) circuit is open, the gauge needle will not move at all. If the ground circuit is open, the gauge needle will move up to its extreme position.

TROUBLESHOOTING HINTS
- Malfunction of the engine coolant temperature gauge unit
- Malfunction of the combination meter (printed-circuit board or engine coolant temperature gauge assembly)
- Damaged harness wires or connectors

DIAGNOSIS

Required Special Tool:
MB991223: Harness Set

STEP 1. Check with other meter.
Check to see that the speedometer, tachometer and engine coolant temperature gauge unit operate normally.

Q: Do all other meters operate?

YES Go to Step 2.

NO Refer to INSPECTION PROCEDURE 5.

STEP 2. Check engine coolant temperature gauge unit connector B-112 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is engine coolant temperature gauge unit connector B-112 in good condition?

YES: Go to Step 3.

NO: Repair or replace the damaged component(s). Refer to Harness Connector Inspection. The engine coolant temperature gauge unit should work normally.

STEP 3. Check the engine coolant temperature gauge unit.
Check to see that the engine coolant temperature gauge unit operate normally. Refer to ENGINE COOLANT TEMPERATURE GAUGE UNIT CHECK.

Q: Is the engine coolant temperature gauge unit normal?

YES: Go to Step 4.

NO: Replace the engine coolant temperature gauge unit. The engine coolant temperature gauge unit should work normally.

STEP 4. Check combination meter connector C-02 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Is combination meter connector C-02 in good condition?

YES: Go to Step 5.

NO: Repair or replace the damaged components). Refer to Harness Connector Inspection. The engine coolant temperature gauge unit should work normally.

STEP 5. Check the wiring harness between engine coolant temperature gauge unit connector B-112 (terminal 1) and combination meter connector C-02 (terminal 50).

NOTE: Also check intermediate connector C-124 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-124 is damaged, repair or replace the connector as described in Harness Connector Inspection.

Q: Are the wiring harness between engine coolant temperature gauge unit connector B-112 (terminal 1) and combination meter connector C-02 (terminal 50) in good condition?

YES: Repair or replace the combination meter. The engine coolant temperature gauge unit should work normally.

NO: Repair the wiring harness. The engine coolant temperature gauge unit should work normally.