Circuit Description
Engine torque information is sent to the transmission control module (TCM) by the engine control module (ECM) through the GMLAN high-speed controller area network (HSCAN). A two-wire circuit is used to communicate data between the ECM and TCM, CAN H and CAN L. A fault in the HSCAN will not cause DTC P1779 to set by itself. If a communication fault occurs, other DTCs will set before P1779.
When the ECM sends the TCM an invalid engine torque signal, DTC P1779 sets. DTC P1779 is a type B DTC.
Conditions for Running the DTC
| • | No HSCAN DTCs U2103, or U2105 |
| • | The engine speed is greater than 300 RPM for 5 seconds. |
Conditions for Setting the DTC
The TCM detects an invalid engine torque signal for 2.0 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | The TCM moves the speed ratio towards a target ratio and then freezes the ratio changes. |
| • | The TCM discontinues use of the closed loop ratio control algorithm. This causes the speed ratio to be defaulted and possibly not accurate. The resulting open loop control may or may not provide optimum ratio performance. |
| • | The TCM commands maximum pressure to the input clutch. |
| • | The TCM defaults to a fixed engine torque value. |
| • | The TCM no longer inhibits shifting to between reverse and drive when moving. |
| • | The TCM freezes garage shift transmission adaptive functions. |
| • | The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records. |
| • | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records. |
| • | The TCM stores DTC P1779 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request. |
| • | A scan tool can clear the MIL/DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring. |
| • | The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls - 2.2L (L61) | ||||
2 |
Important:
Did you record any ECM Failure Records? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 2.2L (L61) | Go to Step 3 | ||||
3 |
Did DTC P1779 reset? | -- | Go to Step 4 | Go to Intermittent Conditions in Engine Controls - 2.2L (L61) | ||||
4 | Did any other DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 2.2L (L61) | Go to Step 5 | ||||
5 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 2.2L (L61). Is the action complete? | -- | Go to Step 6 | -- | ||||
6 | Perform the following operation to verify the repair:
Has the test run and passed? | -- | Go to Step 7 | Go to Step 2 | ||||
7 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 2.2L (L61) | System OK |
