Automatic transmission control unit (Transmission Control Module, TCM)
Purpose
The Transmission Control Module (TCM) is an electronic device that controls gear shifting and other functions of an automatic transmission (AT).
Location
Typically the TCM is installed in or near the automatic transmission housing.
Components
The main components of TCM include:
* Microprocessor: Controls gear shift logic and other functions.
* Memory: stores programs and gear shift maps.
* Input sensors: read information about engine, transmission and vehicle parameters.
* Output actuators: control solenoid valves, solenoids and other automatic transmission devices.
Functions
TCM performs the following functions:
* Optimally shifts gears based on engine speed, load and other parameters.
* Locks the torque converter to improve transmission efficiency.
* Controls the Kickdown function to provide faster gear shifting.
* Diagnoses automatic transmission faults and sets trouble codes (DTCs).
* Adapts to driving style and traffic conditions to improve gear shifting.
Malfunctions
TCM malfunctions can cause a variety of automatic transmission problems, including:
* Incorrect gear shifting
* Delay or slippage of gears
* Vibration or shock when shifting gears
*Transmission fluid leak
* Constantly flashing Check Engine light
Diagnostics
Diagnosis of TCM faults is usually done using an OBD-II scanner. The scanner can read trouble codes and parameter information stored in the TCM.
Repair
In most cases, a faulty TCM will need to be replaced. Replacing the TCM is a complex process that should be performed by a qualified mechanic.