Circuit Description
To improve shift feel, the transmission control module (TCM) may request that the engine control module (ECM) reduce engine torque during shift events. When such a request is received, the ECM responds by retarding the base ignition timing and notifying the TCM that the request has succeeded. If the ECM is unable to comply with the request, the ECM sends the TCM a message that the request has failed.
The torque reduction request is sent to the ECM through a communication network called the controller area network (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P1780 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1780.
When the TCM receives a torque reduction failure message from the ECM, then DTC P1780 will set. DTC P1780 is a type A DTC.
Conditions for Running the DTC
| • | No CAN DTC U2105. |
| • | The ignition voltage is 8-18 volts. |
| • | The engine run time is 3 seconds or greater. |
| • | Trans. Protection Mode is OFF. |
Conditions for Setting the DTC
The ECM notifies the TCM that a torque reduction request has failed for 0.8 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL). |
| • | The TCM increases line pressure control solenoid valve (SLT). |
| • | The line pressure is at maximum, and freezes the transmission adapt functions. |
| • | 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 records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record. |
| • | The TCM stores DTC P1780 in TCM history. |
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 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 P1780 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 |
