P1643

CIRCUIT DESCRIPTION
A Wait-to-start indicator is illuminated by the Engine Control Module (ECM) when the glow plugs are commanded ON. When the ECM is commanding the Wait To Start indicator ON, the voltage potential of the circuit will be low, near 0 volts. When the ECM is commanding the Wait To Start indicator OFF, the voltage potential of the circuit will be high (near battery voltage). The primary function of the ECM is to supply the ground for the Wait To Start indicator control circuit.

CONDITIONS FOR RUNNING THE DTC
^ The ignition is in the ON.
^ The ignition voltage is between 6-18 volts.

CONDITIONS FOR SETTING THE DTC
The voltage on the Wait To Start indicator circuit is high (near battery voltage) when the Wait To Start indicator is requested ON.

or

The voltage on the Wait To Start indicator control circuit is low (near 0 volts) when the Wait To Start indicator is requested OFF.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
^ A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
A faulty bulb or the control circuit shorted to ground will cause a Diagnostic Trouble Code (DTC) P1643 to set.

TEST DESCRIPTION

Steps 1-11:

The numbers below refer to the step numbers on the diagnostic table.
2. The Wait-to-Start indicator is illuminated briefly when the ignition is turned ON. The on time depends on the temperature of the engine at that time.
5. If the fuse opens during this test, there is a short to voltage on the control circuit.
9. If no trouble is found in the control circuit or the connection at the ECM, the ECM maybe malfunctioning.