Transmission Control Module (Tcm)

DESCRIPTION
The Transmission Control Module (TCM) is an electronic device which monitors various inputs in order to control various transmission functions. These functions include shift timing and quality, TCC apply and release, line pressure, and transmission diagnostics. The TCM receives input from electrical sensors, switches, solenoids and other components in order to process for use within the control program of the TCM. Based on this input information, the TCM controls certain transmission output functions and devices. The TCM is located behind the kick panel beneath the glove compartment, in the passenger compartment.

DATA LINK CONNECTOR (DLC)
The DLC is a 16-pin connector that provides the technician a means of accessing serial data for aid in diagnosis. This connector allows the technician to use a scan tool in order to monitor the various system parameters and display the Diagnostic Trouble Code (DTC) information. The DLC is located within the driver[prime ]s compartment, underneath the dash on the driver[prime ]s side.

Serial Data
This model uses ISO serial data and communicates with the scan tool on DLC pin 7. Most other GM OBD II vehicles use Class 2 serial data on DLC pin 2. Both the ECM and the TCM communicate with the scan tool by using the ISO serial data circuit.

SERVICE TRANSMISSION LAMP (STL)
The TCM controls a dedicated Service Transmission Lamp (STL) which illuminates when certain non-emissions driveability conditions which relate to the TCM diagnostics report a fail. The Service Transmission Lamp (STL) is located in the Instrument Panel Cluster (IPC).

The TCM has no direct control of the engine MIL, but if a transmission fault occurs that is emissions related, the engine MIL must illuminate. A MIL Request circuit between the ECM and the TCM provides a means for illuminating the MIL, even though the fault was detected by the TCM. This circuit is pulled up to B+ within the ECM. In order to illuminate the MIL, the TCM pulls the circuit low. The ECM detects this and DTC P1700 is set (in the ECM), which illuminates the MIL.

INPUTS
The TCM uses the following information sensors in order to gather the data for electronically controlling transmission functions:
- Transmission Fluid Temperature (TFT) sensor
- Transmission Range Switch
- Output Speed Sensor

Certain additional signals are sent between the ECM and the TCM on dedicated circuits for each signal.