Circuit Description
A dash light (wait to start) is illuminated by the PCM when the glow plugs are commanded ON. When the PCM is commanding the wait to start lamp ON, the voltage potential of the circuit will be low (near 0 volts). When the PCM is commanding the wait to start lamp OFF, the voltage potential of the circuit will be high (near battery volts). The primary function of the PCM is to supply the ground for the wait to start lamp circuit.
Conditions for Running the DTC
Voltage on wait to start lamp circuit high (near battery volts).
or
Voltage on wait to start lamp control circuit low (near 0 volts).
Conditions for Setting the DTC
Wait to start lamp requested ON.
or
Wait to start lamp requested OFF.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after three consecutive trips without a fault condition. |
| • | A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | Use of a scan tool |
Diagnostic Aids
Important: Remove any debris from the PCM module connector surfaces before servicing the PCM module. Inspect the PCM module connector gaskets when diagnosing/replacing the module. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM module.
A faulty bulb or the control circuit shorted to ground will cause a P1643 to set.
