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 (CAN). Two circuits are used to communicate CAN data between the ECM and TCM. A fault in the CAN will not cause DTC P1781 to set by itself. If a CAN fault occurs, other DTCs will set before DTC P1781.
When the ECM sends the TCM an engine torque signal that is below the lower limit, above the upper limit, or is an unreliable value, then DTC P1781 will set. DTC P1781 is a type C DTC.
Condition for Running the DTC
The ignition is ON.
Condition for Setting the DTC
Engine torque signal is below the lower limit, above the upper limit, or is an unreliable value for 1 second.
Action Taken When the DTC Sets
| • | The TCM flashes the sport mode lamp. |
| • | The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM records this information as Failure Records. |
| • | The TCM stores DTC P1781 in TCM history. |
Conditions for Clearing the MIL/DTC
| • | The TCM stops flashing the sport mode lamp as soon as the fault is no longer present. |
| • | A scan tool can clear the DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-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 | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission ? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission | |||||||||
2 |
Important: Record all Failure Records before clearing the DTC. Using Clear Info erases the Failure Records from the ECM and TCM. Did you record any ECM Failure Records? | -- | Go to the applicable ECM DTC | |||||||||
3 | Did you record Failure Records for any of the following DTCs?
| -- | Go to the applicable CAN Bus DTC | |||||||||
4 |
Did DTC P1781 reset? | -- | Go to Intermittent Conditions in Engine Controls | |||||||||
5 | Did any other DTCs set? | -- | Go to the applicable DTC | |||||||||
6 | Replace the ECM. Refer to Engine Control Module Replacement . Is the action complete? | -- | -- | |||||||||
7 | Perform the following operation to verify the repair:
Did DTC P1781 reset? | -- | System OK |
