Temperature Switch (Warning Indicator): Testing and Inspection

The diagnosis found here addresses an inoperative lamp condition.

If the problem being diagnosed is related to lamp accuracy, be certain to confirm that the problem is with the lamp and not with cooling system performance.

The actual engine coolant temperature should be checked with a test gauge or thermometer before proceeding with lamp diagnosis.

1. Turn the ignition switch to the ON position.

Typical Coolant Temperature Switch/Sending Unit:

Disconnect the coolant temperature switch connector as shown.

Note: The image shows a typical coolant temperature switch/sending unit.

Install a jumper wire between the switch connector and a good ground. The lamp should light.
If OK, replace the faulty switch.
If not OK. go to Step 2.
2. Turn the ignition switch to the OFF position.
Disconnect the battery negative cable.
Unplug the coolant temperature switch connector.
Remove the instrument cluster bezel and the cluster assembly.
Disconnect the cluster connector.
Check for continuity between the engine coolant temperature (ECT) sensor signal circuit cavity of the cluster connector
and a good ground. There should be no continuity.
If OK, go to Step 3.
If not OK, repair the short circuit as required.
3. Check for continuity between the engine coolant temperature (ECT) sensor signal circuit cavity of the cluster connector and the coolant temperature switch connector. There should be continuity.
If OK, replace the faulty bulb.
If not OK, repair the open circuit as required.