Wait To Start Light: Description and Operation

WAIT - TO - START INDICATOR

DESCRIPTION
A wait-to-start indicator is standard equipment in all instrument clusters. The wait-to-start indicator is located near the lower edge of the instrument cluster, to the right of the multi-function indicator display. The wait-to-start indicator consists of the International Control and Display Symbol icon for "Diesel Preheat" imprinted within a rectangular cutout in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the icon to appear silhouetted against an amber field through the translucent outer layer of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board. The wait-to-start indicator is serviced as a unit with the instrument cluster.

OPERATION
The wait-to-start indicator gives an indication to the vehicle operator when the diesel 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 Engine Control Module (ECM) 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 detects that the ignition switch is in the On position. Therefore, the LED will always be off when the ignition switch is in any position except On. 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:

- Bulb Test - Each time the ignition switch is turned to the On position the wait-to-start indicator is illuminated for about two seconds as a bulb test.
- Wait-To-Start Lamp-On Message - Each time the cluster receives a wait-to-start lamp-on message from the ECM indicating that the diesel engine glow plugs are energized in their pre-heat operating mode, the wait-to-start indicator will be illuminated. The indicator remains illuminated until the cluster receives a wait-to-start lamp-off message indicating that the pre-heat mode of the glow plugs has been completed, until the ECM detects that the engine is running, or until the ignition switch is turned to the Off position, whichever occurs first.

The ECM continually monitors the engine coolant temperature sensor to determine when the glow plugs need to be energized in their pre-heat operating mode. The ECM then sends the proper wait-to-start lamp-on and lamp-off messages to the instrument cluster. If the instrument cluster turns on the indicator after the engine is started, it may indicate that a malfunction has occurred and that the engine glow control system requires service. The ECM will store a Diagnostic Trouble Code (DTC) for any malfunction it detects. For proper diagnosis of the engine coolant temperature sensor, the engine glow control system and circuits, the ECM, the CAN data bus, or the electronic message inputs to the instrument cluster that control the wait-to-start indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.