Temperature Gauge: Description and Operation
ENGINE TEMPERATURE GAUGEAn engine coolant temperature gauge is standard equipment on all instrument clusters. The engine coolant temperature gauge is located in the lower right corner of the instrument cluster, to the right of the speedometer. 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 gauge dial face that reads left-to-right from 40 - 125 °C, or from 100 - 260 °F, depending upon the market for which the vehicle is manufactured. An International Control and Display Symbol icon for "Engine Coolant Temperature" is located on the gauge dial face directly below the left end of the gauge scale.
The engine coolant temperature gauge graphics are either white, gray and orange against a black gauge dial face (base cluster) or black, gray and red against a taupe gauge dial face (premium cluster), 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 base cluster white gauge graphics appear blue-green and the orange graphics still appear orange, while the premium cluster taupe gauge dial face appears blue- green with the black graphics silhouetted against the illuminated background and the red graphics still appear red. The gray gauge graphics for both versions of the cluster are not illuminated. The orange gauge needle in the base cluster gauge is internally illuminated, while the black gauge needle in the premium cluster gauge is not.
Base cluster gauge illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit board. Premium cluster gauge illumination is provided by an integral electro-luminescent lamp that is serviced as a unit with the instrument cluster. 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 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 is completely controlled by the instrument cluster electronic circuit board. 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 Normal Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is within the normal operating range [up to about 124 °C (255 °F) for gasoline engines, or about 115 °C (239 °F) for diesel engines], the gauge needle is moved to the actual relative temperature position of the gauge scale.
- Engine Temperature High Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is high [above about 127 °C (260 °F) for gasoline engines except Gulf Coast Country (GCC), 129 °C (264 °F) for GCC gasoline engines, or 118 °C (244 °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 a message from the PCM indicating the engine coolant temperature is critical [above about 132 °C (269 °F) for gasoline engines, or 126 °C (259 °F) for diesel engines], the gauge needle is moved to the high end of the red warning zone on the gauge scale.
- Communication Error - If the cluster fails to receive an engine temperature message, it will hold the gauge needle at the last indication for about 12 seconds or until the ignition switch is turned to the Off position, whichever occurs first. After twelve 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 across the entire gauge scale and back 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 Instrument Cluster Diagnosis and Testing. 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 PCI data bus, or the electronic message inputs to the instrument cluster that control the engine coolant temperature gauge, a DRBIII scan tool is required Refer to the appropriate diagnostic information.