GM/Detroit 6.5L ENGINE CONTROLS – DTC P1643 Wait to Start Lamp Control Circuit

Refer to Glow Plug Controls

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 voltage). The primary function of the PCM is to supply the ground for the Wait To Start lamp circuit.

Conditions for Running the DTC
The ignition switch is in the ON position.

Conditions for Setting the DTC
The voltage on the Wait To Start lamp circuit is high (near battery voltage) when the Wait To Start lamp is requested ON.
or
The voltage on the Wait To Start lamp control circuit is low (near 0 volts) when the Wait To Start l amp is 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 rel ated diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
A faulty bulb or the control circuit shorted to ground will cause a P1643 to set.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. Repeat the command as many times as necessary (when glow plugs are commanded ON by the scan tool, an internal PCM timer protects the glow plugs from damage by cycling them ON for 3 seconds and OFF for 12 seconds. After the 12 seconds has elapsed, the glow plugs can be commanded ON again).
9. I f no trouble is found in the control circuit or the connection at the PCM, the PCM maybe malfunctioning, however, this is an extremely unlikely failure.

 

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