Transmission Control Module (TCM) Inputs/Outputs

Transmission Control Module Inputs and Outputs:

The TCM receives inputs from the transmission, fuel injection and ignition ECMs, external components, and other vehicle systems and applies them to the operating strategy to determine the optimum transmission control outputs.

INPUTS:

Mode switch: The mode switch position inputs the driver's choice of operating strategy to the TCM.

Input and output speed sensors: The TCM uses the transmission input and output speeds to help determine line pressure, shift patterns, and torque converter lock-up clutch apply pressure and timing. The speed inputs are also used to calculate turbine speed, deviation from gear ratio, and lock-up clutch slippage for diagnostic purposes and "adaptive learning" functions.

Transmission fluid temperature: The TCM monitors the transmission fluid temperature to help determine torque converter lock-up clutch operation and line pressure. The TCM inhibits lock-up clutch operation until the fluid temperature reaches approximately 68°F (20°C).

If the fluid temperature becomes excessively high (approximately 250°F [122°C]), the TCM will apply the lock-up clutch whenever the transmission is in Second, Third or Fourth gears. Applying the lock-up clutch serves to reduce the fluid temperature, as the torque converter fluid coupling is bypassed.

Above approximately 310°F (154°C), the TCM will flag a fluid temperature diagnostic trouble code (DTC). Once the DTC is flagged, the TCM assumes a fixed temperature input of 266°F (130°C) and applies the lock-up clutch in Second, Third and Fourth gears.

Force motor feedback: The TCM senses the force motor duty cycle (percent time energized) to determine the prevailing transmission line pressure.

Pressure switch manifold: The pressure switch manifold output logic is used by the TCM to determine what gear range (PRN[D]D32) the transmission is operating in.

Kick down: A kick down ground input is supplied to the TCM when the driver activates the switch by depressing the accelerator to the kick down position.

Engine throttle position: A variable voltage input allows the TCM to sense throttle position. Throttle position, and other sensor inputs, are used to determine shift patterns and torque converter lock-up clutch apply and release. In general, the greater the throttle opening, the higher the upshift speeds and the greater the transmission line pressure. The TCM releases the lock-up clutch at minimum throttle opening and during open-throttle heavy acceleration.

Barometric pressure sensor: The barometric pressure input allows the TCM to adjust the line pressure for changes in air density that affect engine power.

Engine speed: An engine speed input is supplied to the TCM from the ignition ECM. Engine speed is one of the sensed inputs used to determine shift patterns and torque converter lock-up clutch apply and release.

Brake operation: The TCM receives a brakes applied input via the stop light relay. When the brakes are applied, the TCM releases the torque converter lock-up clutch.

A/C compressor clutch operation: The TCM receives a compressor clutch operating input from the climate control module compressor clutch relay activation circuit. When the compressor is operating, the TCM adjusts the line pressure and shift timing to compensate for the added engine load.

EMS fuel fail: If a fuel fail input is received from the fuel injection ECM, the TCM defaults to a higher line pressure to compensate for the loss of engine power.

OUTPUTS:

Force motor (line pressure): The TCM varies the current to the force motor to control "torque signal" pressure, which in turn, controls line pressure. The lower the "torque signal" pressure, the lower the line pressure; the higher the "torque signal" pressure, the higher the line pressure. At idle (throttle closed), current flow is close to maximum, positioning the force motor so that minimum "torque signal" pressure is applied to the line pressure regulator. At full throttle, current flow is close to minimum, positioning the force motor so that maximum "torque signal" pressure is applied to the line pressure regulator.

If the electrical system becomes disabled, current flow to the force motor will stop and maximum "torque signal" pressure will he applied creating maximum line pressure, thus preventing component slippage until the condition can be corrected.

Gear shift solenoids A and B: The TCM controls the shift solenoids, based on parameters defined by the operating strategy, by switching the solenoid coil ground circuits. The following table shows the solenoid state combination required for each gear range:

Gear Range Solenoid A Solenoid B

P,R,N ON OFF

First ON OFF

Second OFF OFF

Third OFF ON

Fourth ON ON

Torque converter clutch (TCC) solenoid: The rate at which the torque converter lock-up clutch is applied depends on the torque converter clutch signal pressure as controlled by the duty cycle of the TCC solenoid. The TCM varies the duty cycle of the TCC solenoid by controlling the ground circuit. The TCC solenoid, in turn, varies the torque converter clutch signal pressure acting on the lock-up clutch shift valve. By varying the duty cycle of the TCC solenoid, lock-up clutch apply and release occurs smoothly.

Ignition retard request and acknowledge: When the TCM senses that a reduction in engine torque is required to allow a "quality shift", a request for ignition retard is output to the ignition ECM. After the ignition has been retarded, the ignition ECM signals the TCM to acknowledge timing retard. When the acknowledgment is received, the TCM initiates the apply or release function.