OPERATION

The engine coolant temperature gauge gives an indication to the vehicle operator of the engine coolant temperature. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Controller Area Network (CAN) data bus.

The engine coolant temperature gauge is driven by an electronic stepper motor unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

• Engine Temperature Message - Each time the cluster receives an electronic engine temperature message from the PCM indicating the temperature is between the low end of normal [about 41 degrees C (105 degrees F) for gasoline engines, or about 28 degrees C (82 degrees F) for diesel engines] and the high end of normal [about 124 degrees C (255 degrees F) for gasoline engines, or about 124 degrees C (256 degrees F) for diesel engines], the gauge needle is moved to the actual relative temperature position on the gauge scale.
• Engine Temperature Low Message - Each time the cluster receives an electronic engine temperature message from the PCM indicating the temperature is low [at or below about 40 degrees C (104 degrees F) for gasoline engines, or about 27 degrees C (81 degrees F) for diesel engines], the gauge needle is held below the graduation on the far left end of the gauge scale. The gauge needle remains below the low end of the gauge scale until the cluster receives a message from the PCM indicating that the temperature is above the low end of normal, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Engine Temperature High or Critical Message - Each time the cluster receives an electronic engine temperature message from the PCM indicating the temperature is high [at or above about 127 degrees C (261 degrees F) for gasoline engines, or about 128 degrees C (262 degrees F) for diesel engines], the gauge needle is moved to the red graduation at the high end of the gauge scale, the engine temperature indicator is illuminated and a single chime tone is sounded. The gauge needle remains at the red graduation and the engine temperature indicator remains illuminated until the cluster receives a message from the PCM indicating that the temperature is below about 124 degrees C (255 degrees F), or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the engine temperature indicator is cycled OFF and then ON again by the appropriate messages from the PCM.
• Communication Error - If the cluster fails to receive an engine temperature message, it will hold the gauge needle at the last indication for about five seconds or until the ignition switch is turned to the OFF position, whichever occurs first. After five seconds, the cluster will move the gauge needle to the low end of the gauge scale.
• Actuator Test - Each time the cluster is put through the actuator test, the engine coolant temperature gauge needle will be swept to several calibration points on the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM then sends the proper messages to the ElectroMechanical Instrument Cluster (EMIC). If the instrument cluster turns ON the engine temperature indicator due to a high or critical engine coolant temperature gauge reading, it may indicate that the engine or the engine cooling system requires service.

For proper diagnosis of the engine coolant temperature sensor, the PCM, the EMIC, the CAN data bus or the electronic communication related to engine coolant temperature gauge operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.