Circuit Description
Engine torque information is sent to the Transmission Control Module (TCM) by the Engine Control Module (ECM) through a communication network called the Controller Area Network (GMLAN). Two circuits are used to communicate GMLAN data between the ECM / TCM and other modules. A fault in the GMLAN will not cause DTC P2637 to set by itself. If a GMLAN fault occurs, other DTCs will set before DTC P2637.
When the ECM sends the TCM an engine torque signal is invalid, DTC P2637 will set, which is a type 'B' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8.0 and 18.0 volts. |
| • | Engine is running between 450 and 6,800 RPM at least 5 seconds. |
| • | No other GMLAN errors are present. |
Conditions for Setting the DTC
The ECM GMLAN message does not contain a valid engine torque value for 2 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the Powertrain Interface Module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL) in the instrument cluster during the second consecutive drive trip in which the 'Conditions for setting the DTC' are met. |
| • | At the time of the first failure, the TCM records the operating conditions when the 'Conditions for setting the DTC' are met. The TCM stores this information as a failure record. |
| • | At the time of the second failure, the ECM records the operating conditions when the 'Conditions for setting the DTC' are met. The ECM stores this information as a freeze frame. |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P2637 into TCM history. |
| • | The TCM also turns off the pressure control solenoid (causing maximum line pressure). |
| • | The TCM inhibits autograde braking and shift stabilization. |
Conditions for Clearing the MIL/DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the default actions when the ignition is off long enough to power down the TCM. |
| • | The PIM turns off the Check Powertrain MIL after the sixth consecutive drive trip in which the TCM does not send a Check Powertrain MIL illumination request. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | ||||||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | -- | Go to Step 2 | |||||
2 |
Did you record any ECM DTCs? | -- | Go to Step 3 | |||||
3 |
Did DTC P2637 reset? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections | ||||
4 | Did any other DTCs set? | -- | Go to Step 5 | |||||
5 | Replace TCM. Refer to Transmission Control Module Replacement. Is the replacement complete? | -- | Go to Step 6 | -- | ||||
6 |
Has the test run and passed? | -- | System OK | Go to Step 2 | ||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||||||
