Transmission Control Module
A microcomputer controls the transmission by receiving and processing signals from various switches and sensors. The microcomputer determines shift sequences, shift timing, and clutch apply and release characteristics. The microcomputer is an independent controller and is referred to as the Transmission Control Module (TCM). See Fig 1. TCMs are available in 12-volt configurations to match the configuration of the vehicle electrical system. The pressure switch manifold and Park/Neutral Position (PNP) switch provide operator input to the TCM. Other data sent to the TCM include throttle position; engine, turbine, and output speeds; and sump temperature. Any active special function, such as anti-lock brakes or power takeoff, is also an input to the TCM. The TCM processes this data to determine proper shift points, to monitor the current gear range, to perform ratio tests, and to compile diagnostic data. The TCM is programmed to protect the transmission and other vehicle driveline components by inhibiting actions such as full-throttle shifts from Neutral and high-speed direction changes. The TCM determines if a system malfunction exists and stores Diagnostic Trouble Codes (DTC) related to the malfunction. The codes, accessed by the service technician, are used in diagnosing persistent or intermittent trouble in the system.