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GM/Detroit 6.5L – Engine Management – TRANSMISSION CONTROL – System Operation

Non-EFI 6.5L diesels equipped with the 4L80E transaxle use a dedicated Transmission Control Module (TCM) to provide shift control timing, TCC apply and release, and line pressure control. The TCM has been eliminated on 6.5L EFI vehicles.
Its duties are now performed by the PCM. PCM inputs and outputs for transmission control for the 4L60E and 4L80E are listed in figures 5-54 and 5-55, respectively.

The PCM also stores diagnostic trouble codes (DTCs) for the transmission. Some codes are shared by the engine and PCM, while others are dedicated transmission codes. The list of 6.5L EFI codes identifies shared as well as transmission only codes.
Because the focus of this course is 6.5L EFI engine management, the only components of transmission control to be discussed, other than those already included in other subsystems, are the output speed sensor and the vehicle speed sensor (VSS). They have the most direct impact on engine control fuel delivery.

For complete coverage of 4L80E and 4L60E operation, diagnosis, and service procedures, refer to the following GM training center courses:
• #17001.17: Hydra-Matic 4L80E
• #17007.18: Hydra-Matic 4L60E


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