Control Module: Description and Operation

The Transmission Control Module (TCM) is separate from the Powertrain Control Module (PCM). Both control modules are used to determine the operational characteristics of the transaxle, such as shift timing or lockup. These characteristics are calculated with a series of switch and sensor inputs to produce optimum driveability.

SELF DIAGNOSIS FUNCTION
The TCM has a self diagnosis function which monitors the electrical circuits of certain sensors and solenoids. These are:
- Coasting clutch solenoid.
- Line pressure solenoid.
- Transmission Range (TR) switch.
- Shift solenoid A.
- Shift solenoid B.
- Throttle Position (TP) sensor.
- Torque Converter Clutch (TCC) solenoid.
- Vehicle Speed Sensor (VSS).
- Pulse Signal Generator (PSG) (Turbine Shaft Speed (TSS) sensor).
This self diagnosis function is a function of the fail safe control system. When one of these sensor or solenoid circuit readings is out of range, then the self diagnosis function places the 4F20E automatic transaxle in the fail safe mode.

FAIL SAFE FUNCTION
The 4F20E automatic transaxle is equipped with a fail safe control system. If the vehicle sustains damage to one of the components listed below, the fail safe function is activated. The fail safe action is controlled by the TCM. Fail safe operation can be detected by observing the OVERDRIVE (O/D) OFF lamp. The O/D OFF lamp will blink for approximately eight seconds when the ignition switch is turned ON.








NOTE: Fail safe may be activated even if no electrical circuits are damaged. An example of this condition is excessive wheel spin. If this occurs the vehicle will be placed in third gear and remain in third until the ignition switch is cycled. Once the ignition switch is cycled, the fail safe action will be deactivated and the vehicle will return to its normal shift pattern.