Procedure 4 - Coolant Temp Gauge Inoperative

Engine Coolant Temperature Gauge does not Work

Engine Coolant Temperature Gauge Circuit:

Connectors:

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
- 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 the speedometer operation.

Q: Does the speedometer work normally?

YES: Go to Step 2.

NO: Refer to Inspection Procedure 1.




STEP 2. Check the engine coolant temperature signal circuit at engine coolant temperature connector B-112 by backprobing.
1. Do not disconnect engine coolant temperature connector B-112.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 1 and ground by back probing.

Q: Is the voltage approximately 9 volts or more?

YES: Go to Step 5.

NO: Go to Step 3.







STEP 3. Check engine coolant temperature gauge unit connector B-112 and combination meter connector C-02 for damage.

Q: Are engine coolant temperature gauge unit connector B-112 and combination meter connector C-02 in good condition?

YES: Go to Step 4.

NO: Repair or replace it. Refer to Harness Connector Inspection. The engine coolant temperature gauge should work normally.










STEP 4. Check the harness wires between engine coolant temperature gauge unit connector B-112 and combination meter connector C-02.

NOTE: After checking intermediate connector C-124, check the wire. If intermediate connector C-124 is damaged, repair or replace it. Refer to Harness Connector Inspection.

Q: Are the harness wires between engine coolant temperature gauge unit connector B-112 and combination meter connector C-02 in good condition?

YES: Repair or replace the combination meter (printed-circuit board or engine coolant temperature gauge assembly). The engine coolant temperature gauge should work normally.

NO: Repair them. The engine coolant temperature gauge should work normally.




STEP 5. Check the engine coolant temperature gauge unit.
1. Drain the engine coolant. (Refer to Maintenance Service - Engine Coolant.)
2. Remove the engine coolant temperature gauge unit.
3. Immerse the unit in 78 °C (150 °F) water to measure the resistance.

Q: Is the resistance 104 ± 13.5 Ohm?

YES: Repair or replace the combination meter (printed-circuit board or engine coolant temperature gauge assembly). The engine coolant temperature gauge should work normally.

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