GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2005 🢒 L300/LW300 🢒 Brakes 🢒 Park Brake 🢒 DTC P1779

Circuit Description

Engine torque information is sent to the transmission control module (TCM) by the engine control module (ECM) through the controller area network (CAN). A two-wire circuit is used to communicate data between the ECM and TCM, CAN H and CAN L. A fault in the CAN 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, DTC P1779 sets. DTC P1779 is a type A DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1779 Torque Delivered Signal

Conditions for Running the DTC

No other CAN errors are present.

Conditions for Setting the DTC

The engine torque is invalid for 1 second.

Action Taken When the DTC Sets
    • The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL).
    • The TCM commands maximum line pressure.
    • The TCM freezes 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.

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

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition with the engine OFF.

    3. Important: 

       • Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from both the ECM and the TCM.
       • Record the DTC Freeze Frame and Failure Records.

  3. Record the DTC Failure Records.

Did you record any ECM Failure Records?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 3

3
  1. Clear the DTC.
  2. Turn the ignition OFF for at least 30 seconds.
  3. Start the engine and allow it to idle.

Did DTC P1779 set again?

Go to Step 4

Go to Intermittent Conditions in Engine Controls - 3.0L (L81)

4

Did any other DTCs set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

Go to Step 5

5

Replace the TCM.

Refer to Control Module References in Computer/Integrating Systems for replacement, set-up, and programming.

Is the action complete?

Go to Step 6

--

6

Perform the following operation to verify the repair:

  1. Select DTC on the scan tool.
  2. Select Clear Info.
  3. Start the engine and allow it to idle.
  4. Select Specific DTC.
  5. Enter DTC P1779.

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 - Vehicle in Vehicle DTC Information

System OK