Temperature Gauge: Description and Operation

An engine coolant temperature gauge is used only in the highline instrument clusters. The engine coolant temperature gauge is located in the right lower quadrant of the instrument cluster, below the oil pressure gauge. The engine coolant temperature gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree scale on the cluster overlay that reads left-to-right from 40 °C (or 100 °F) to 125 °C (or 260 °F). An International Control and Display Symbol icon for "Engine Coolant Temperature" is located on the cluster overlay above the left end of the gauge scale. The gauge needle, gauge scale, and icon are clearly visible on the face of the instrument cluster in daylight, and are illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting when the exterior lamps are turned ON. Cluster illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit board. The engine coolant temperature gauge is serviced as a unit with the instrument cluster.

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 the cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Chrysler Collision Detection (CCD) 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 (st-run) 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 High Message- Each time the cluster receives a message from the PCM indicating the engine coolant temperature is about 124 °C or higher (about 255 °F or higher), the gauge needle is moved to the beginning of the red zone on the gauge scale, the check gauges indicator is illuminated, and a single chime tone is sounded. The chime tone feature will occur only once per ignition cycle. The gauge needle remains in the red zone and the check gauges indicator remains illuminated until the cluster receives a message from the PCM indicating that the engine temperature is about 122 °C or lower (about 252 °F or lower), or until the ignition switch is turned to the OFF position, whichever occurs first.
- Engine Temperature Critical Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is about 129 °C or higher (about264 °F or higher), the gauge needle is moved to the far right end of the gauge scale. The gauge needle remains at the far right end of the scale until the cluster receives a message from the PCM indicating that the engine temperature is about 127 °C or lower (about 261 °F or lower), or until the ignition switch is turned to the OFF position, whichever occurs first.
- Message Failure - If the cluster fails to receive an engine temperature message, it will hold the gauge needle at the last indication until a new message is received, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the gauge needle will be swept to several calibration points on the gauge scale in a prescribed sequence to confirm the functionality of the gauge and the cluster 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 INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). If the instrument cluster turns ON the check gauges 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 CCD data bus, or the message inputs to the instrument cluster that control the engine coolant temperature gauge, a DRB III scan tool and the appropriate diagnostic information are required.