Circuit Description
The Engine Control Module (ECM) sends engine speed data to the Transmission Control Module (TCM) through a communication network called the GM Local Area Network (GMLAN). Two circuits are used to communicate GMLAN data between the ECM/TCM and other modules. The TCM uses this data to help determine shift patterns and torque converter clutch apply and release.
A fault in the GMLAN will not cause DTC P0727 to set by itself. If a GMLAN fault occurs, other DTCs will set before DTC P0727.
When the TCM receives invalid engine speed data from the ECM, then DTC P0727 sets, which is a type 'B' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8.0 and 18.0 volts. |
| • | The engine is running. |
Conditions for Setting the DTC
The ECM GMLAN message does not contain a valid engine speed 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) during the second consecutive trip in which the 'Conditions for Setting the DTC' have been 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 also turns off the pressure control solenoid (causing maximum line pressure). |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM stores DTC P0727 into TCM history. |
Conditions for Clearing the MIL/DTC
| • | 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. |
| • | 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. |
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 you record a TCM failure record for DTC U0100? | -- | Go to Step 4 | |
4 |
Is the engine speed within the specified range? | 500-1,000 RPM | Go to Step 5 | Go to Step 6 |
5 | Road test the vehicle at various engine speeds. Does DTC P0727 reset? | -- | Go to Step 7 | Go to Testing for Intermittent Conditions and Poor Connections |
6 | Using Tech 2, select Engine Data and scroll to Engine Speed data list parameter and observe the reading. Is the engine speed within the specified range? | 500-1,000 RPM | Go to Step 7 | Go to Step 8 |
7 | Did any other engine related DTCs set? | -- | Go to Step 8 | |
8 | Replace the TCM. Refer to Refer to Transmission Control Module Replacement for replacement procedures. Is the replacement complete? | -- | Go to Step 9 | -- |
9 | Perform the following procedure to verify the repair:
Has the test run and passed? | -- | Go to Step 10 | Go to Step 2 |
10 | With the Tech 2, observe the stored information, capture information and DTC information. Does the Tech 2 display any DTCs that have not been diagnosed and rectified? | -- | Go to the Diagnostic Trouble Code (DTC) List - Vehicle. | System OK |
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | ||||
