Coolant Temperature Indicator
Coolant temperature indicator is controlled by a temperature sensor, which is monitored by Engine Control Module (ECM) or Powertrain Control Module (PCM). With ignition switch in START position, indicator should come on as a bulb test. When engine coolant temperature exceeds a predetermined limit, ECM or PCM will complete indicator ground circuit, allowing indicator light to come on.
NOTE:
If weak coolant or water is used in cooling system, indicator light may not come on when temperature limit is reached.