Engine Temperature

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) or Engine Control Module (ECM), over the 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/ECM indicating the temperature is between the low end of normal [about 41 °C (105 °F) for gasoline engines, or about 41 °C (105 °F) for diesel engines] and the high end of normal, about 122 °C (252 °F) for gasoline engines, or about 116 °C (240 °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/ECM indicating the temperature is low [at or below about 40 °C (104 °F) for gasoline engines, or about 27 °C (81 °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/ECM 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/ECM indicating the temperature is high [at or above about 122 °C (251 °F) for gasoline engines, or about 116 °C (240 °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/ECM indicating that the temperature is below about 122 °C (251 °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/ECM. Should the temperature exceed 125 °C (257 °F) for gasoline engines, 119 °C (246 °F) for diesel engines, the chime will be continuous.
• 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.

The PCM/ECM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM/ECM then sends the proper messages to the cluster. 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.