Operation

OPERATION

The Transmission Control Module controls all electronic operations of the transmission. The Transmission Control Module receives information regarding vehicle operation from both direct and indirect inputs and selects the operational mode of the transmission. Direct inputs are hardwired to and used specifically by the Transmission Control Module. Indirect inputs originate from other components/modules and are shared with the Transmission Control Module via the vehicle Controller Area Network (CAN) bus.

Some examples of direct inputs to the Transmission Control Module are:

- Traction System Relay Output voltage
- Trans Temp Sensor - P/N Switch
- N2 and N3 Speed Sensors

Some examples of indirect inputs to the Transmission Control Module are:

- Controller Area Network (CAN) Bus Modules
- Shift Lever Assembly
- Brake Lamp Switch

Based on the information received from these various inputs, the Transmission Control Module determines the appropriate shift schedule and shift points, depending on the present operating conditions and driver demand. This is possible through the control of various direct and indirect outputs.

Some examples of Transmission Control Module direct outputs are:

- 1-2/4-5 Solenoid
- 2-3 Solenoid
- 3-4 Solenoid
- TCC Solenoid
- Modulation Pressure Solenoid
- Shift Pressure Solenoid
- DRB III(R) Scan Tool Communication
- Sensor Supply Voltage
- Solenoid Supply Voltage

Some examples of Transmission Control Module indirect outputs are:

- Transmission Temperature (to Powertrain Control Module)
- Shift Lever Position (to Powertrain Control Module)

In addition to monitoring inputs and controlling outputs, the Transmission Control Module has other important responsibilities and functions:

- Storing and selecting appropriate Shift Schedules
- System self-diagnostics
- Diagnostic capabilities (with DRB III(R) scan tool)

NOTE: If the TCM has been replaced, the "TCM Quick Learn" procedure must be performed.

BATTERY FEED

The Transmission Control Module is powered through the Traction Control Relay. The adaptive learn values are stored in non-volatile memory and can only be removed using the DRB III(R).

LIMP-HOME MODE

In order to ensure safe driving and to prevent further damage to the automatic transmission, the Transmission Control Module switches to limp-home mode in the event of a critical failure. A diagnostic trouble code assigned to the failure is stored in memory. All solenoid and regulating valves are thus de-energized. The result is that the gear last engaged remains engaged, the modulating pressure and shift pressure rise to the maximum levels, and the torque converter lockup clutch is disarmed. In order to preserve the operability of the vehicle to some extent, the automatic transmission internal hydraulic control can be used to engage second gear or reverse by: stopping the vehicle, switching off the engine, moving the shift selector lever to Park, waiting at least ten seconds, starting the engine, and moving the shift selector lever to drive to access second gear, or moving the shift selector lever to Reverse if needed. The limp-home function remains active until the failure is corrected or the stored diagnostic trouble code is erased. Sporadic failures may also be reset by switching the ignition switch from Off to On.