GM/Detroit 6.5L ENGINE CONTROLS – DTC P1626 VTD Controller Serial Data Circuit

Circuit Description
The Passlock Module receives the code from the hall effect sensor in the steering column and compares it to the code the Passlock module learned at the first power up at the factory. If this code matches the code stored in the Passlock module, the Passlock module will send a fuel continue message to the PCM (The PCM enables fuel injection temporarily until the fue l continue/disable decision is made). If the Passlock module does not send a code or if the PCM doesn’t receive it, the vehicle will not start (start and stall). If the Passlock module and PCM lose communication with each other while the engine is running the Passlock module will Fail-Enable and allow the driver to restart the vehicle on future ignition cycles until communication between the Passlock module and PCM are restored. If the battery is disconnected during this period, the vehicle will lose its FaiMEnable status and will no longer start until communications has been reestablished. If the Passlock module and PCM lose communications with each other while the engine is not running, the Passlock system wil l disable fuel until communication is restored to prevent vehicle theft. In both cases PTC P1626 will be set. The PCM will not disable fuel injection once it has been enabled within a given ignition cycle to prevent stalling as a result of Passlock system faults.

Conditions for Running the DTC
• The vehicle Theft Deterrent (VTD) system is enabled.
• The fuel enable decision point has been reached.

Conditions for Setting the DTC
• The system has Fail-Enabled due to a loss of communications while the engine is running.
• No password (code) message is received by the PCM from the Passlock control module prior to the VTD Fuel Decision Point.

Action Taken When the DTC Sets
• The vehicle will not start.
• The malfunction indicator lamp (MIL) will not illuminate.

Conditions for Clearing the DTC
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
The most likel y cause of DTC P1626 is a loss of serial data communication to the Passlock module. Check for loss of power to the Passlock module or for other causes of communication l oss. Use the Class 2 Circuit Check in the scan tool to determine if the Passlock module is active (Class 2 Message Monitor on the scan tool). Refer to A Diagnostic System Check – Theft Deterrent for further diagnosis.




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