OPERATION

The wait-to-start indicator gives an indication to the vehicle operator when the diesel engine is too cool for efficient and reliable engine starting, and the engine glow plugs are energized in their pre-heat operating mode. This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Controller Area Network (CAN) data bus.

The wait-to-start indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster 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 instrument cluster transistor. The instrument cluster will turn ON the wait-to-start indicator for the following reasons:

• Wait-To-Start Indicator Lamp-On Message - Each time the cluster receives an electronic wait-to-start indicator lamp-ON message from the PCM indicating that the air temperature is too cool for efficient and reliable engine starting and the glow plugs are energized in their pre-heat mode, the wait-to-start indicator will be illuminated. The indicator remains illuminated until the cluster receives a lamp-OFF message from the PCM, until the PCM detects that the engine is running, 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 wait-to-start indicator will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.

The PCM continually monitors the glow plug control circuits to determine when they are energized in their pre-heat operating mode. The PCM then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC).

For proper diagnosis of the glow plug control circuits, the PCM, the EMIC, the CAN data bus or the electronic communication related to wait-to-start indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.