Engine Temperature Indicator
The engine temperature indicator gives an indication to the vehicle operator when the engine temperature gauge reading reflects a condition requiring immediate attention. This indicator is controlled by a transistor on the IPC circuit board based upon IPC programming and electronic messages received by the IPC from the PCM over the CAN data bus.
The engine temperature indicator LED is completely controlled by the IPC logic circuit, and that logic will only allow this indicator to operate when the IPC receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED will always be OFF when the ignition switch is in any position except ON or START. The LED only illuminates when it is provided a path to ground by the IPC transistor. Each time the ignition switch is turned to the ON position the engine temperature indicator is illuminated for about two seconds as a bulb test. The entire bulb test is a function of the PCM. The IPC will turn ON the engine temperature indicator for the following reasons:
- Engine Temperature High or Critical Message - Each time the IPC receives an electronic engine temperature message from the PCM indicating the temperature is high [at or above about 127 °C (261 °F) for gasoline engines, or about 128 °C (262 °F) for diesel engines], the engine temperature indicator will be illuminated and a single chime tone is sounded. The indicator remains illuminated until the IPC receives a message from the PCM indicating that the temperature is below about 124 °C (255 °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, then ON again by the appropriate messages from the PCM.
The PCM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM then sends the proper messages to the IPC. If the IPC turns ON the engine temperature indicator due to a high engine temperature gauge reading, it may indicate that the engine or the engine cooling system requires service.