Engine Temperature Gauge: Operation

WARNING: This page is about a different car, the 2004 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

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 Programmable Communications Interface (PCI) data bus. The engine coolant temperature gauge is an air core magnetic 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 a message from the PCM indicating the engine coolant temperature is between the low end of normal [about 54° C (130° F)] and the high end of normal [about 129° C (264° F)], the gauge needle is moved to the actual relative temperature position on the gauge scale.
Engine Temperature Low Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is below the low end of normal [about 54° C (130° F)], the gauge needle is held at the "C" increment at the far left end of the gauge scale. The gauge needle remains at the far left end of the gauge scale until the cluster receives a message from the PCM indicating that the engine temperature is above about 54° C (130° F), or until the ignition switch is turned to the Off position, whichever occurs first.
Engine Temperature High Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature, is above about 122° C (252° F), the gauge needle is moved into the red zone on the gauge scale, the check gauges indicator is illuminated in a six-gauge cluster or the engine temperature indicator is illuminated in a four-gauge cluster, and a single chime tone is sounded. The check gauges or engine temperature indicator remains illuminated until the cluster receives a message from, the PCM indicating that the engine temperature is below about 122° C (252° 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 check gauges or engine temperature indicator is cycled off and then on again by the appropriate engine temperature 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 forty seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After forty 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 engine coolant temperature messages to the instrument cluster. For further diagnosis of the engine coolant temperature gauge or the instrument cluster circuitry that controls the gauge, (Refer to DIAGNOSIS AND TESTING - INSTRUMENT CLUSTER ). If the instrument cluster turns on the check gauges or engine temperature indicator due to a high engine 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 PCI data bus, or the electronic message inputs to the instrument cluster that control the engine, coolant temperature gauge, a DRBIII(R) scan tool is required. Refer to ELECTRONIC CONTROL MODULES .