ENGINE TEMPERATURE GAUGE
DESCRIPTION
An engine coolant temperature gauge is standard equipment on all instrument clusters. This gauge is located in the lower right corner of the instrument cluster, to the right of the tachometer. The 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 C (or Cold) to H (or Hot). An International Control and Display Symbol icon for Engine Coolant Temperature is located on the cluster overlay, in the center of the gauge directly above the hub of the gauge needle.
The engine coolant temperature gauge text and graphics are white against a black field, while the major and minor scale increments are black against a silver field, except for a pair of red zone increments at the far right (Hot) end of the gauge scale, making them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the exterior lamps turned ON, the white text and graphics and the major black increments appear blue-green, while the major red increments still appear red. The minor increments are not illuminated. The red gauge needle has internal optical illumination. Gauge 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.
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 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 an electronic engine temperature message from the PCM indicating the temperature is within the normal operating range [up to about 124° C (255° F) for gasoline engines, or about 110° C (230° F) for diesel engines], the gauge needle is moved to the actual relative temperature position on the gauge scale.
- Engine Temperature High Message - Each time the cluster receives an electronic engine temperature message from the PCM indicating the engine coolant temperature is high [above about 127° C (260° F) for gasoline engines, or 112° C (233° F) for diesel engines], the gauge needle is moved into the center of the red warning zone on the gauge scale.
- Engine Temperature Critical Message - Each time the cluster receives an electronic engine temperature message from the PCM indicating the engine coolant temperature is critical [above about 132° C (269° F) for gasoline engines, or 115° C (239° F) for diesel engines], the gauge needle is moved to the high end of the red warning zone on 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 gauge 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 moves the engine coolant temperature gauge needle to indicate a high or critical engine temperature, 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 PCI 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.