GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Vivant 🢒 HVAC 🢒 HVAC - Automatic 🢒 DTC P1779

Circuit Description

The transaxle control module (TCM) is an electronic device which monitors inputs to control various transaxle functions including shift quality and transaxle sensors, switches, and components to process for use within its control program. Based on this input information, the TCM controls various transaxle output functions and devices.

Information is transmitted between the TCM and engine control module (ECM) through the controller area network (CAN). Information is as follows:

    • The engine malfunction signal
    • The engine speed
    • The engine output torque reduction signal
    • The engine coolant temperature

Conditions for Setting the DTC
    • The system voltage is too high or too low.
    • The TCM or ECM is defective.

Action Taken When the DTC Sets
    • No lamp control is required, but diagnostic information should be stored immediately when the malfunction is detected.
    • An adjustable value, calculated over the substitute map engine torque, such as the throttle position or engine speed

Conditions for Clearing the DTC

Using a scan tool can clear history DTCs.

Diagnostic Aids
    • Inspect the poor wiring harness connection for the TCM connectors and transaxle wiring connectors.
    • Inspect the improperly formed or damaged terminals.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install the scan tool.
  2. Turn the ignition ON.
  3. Observe the throttle position value on the scan tool.

Is the throttle position sensor (TPS) within the specified values?

0-100%

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the transmission control module (TCM) wiring connector and electronic control module (ECM) wiring connector.
  3. Measure the resistance between terminal A8 of the TCM wiring connector and terminal 41 of the ECM wiring connector.
  4. Measure the resistance between terminal A16 of the TCM wiring connector and terminal 22 of the ECM wiring connector.

Is the resistance within the specified value?

0 ohms

Go to Step 5

Go to Step 4

4

Repair the malfunctioning terminals as necessary.

Did you complete the repair?

--

System OK

--

5
  1. Turn the ignition ON.
  2. Measure the voltage of terminal A8.
  3. Measure the voltage of terminal A16.

Is the voltage within the specified values?

11-14 V

Go to Step 6

Go to Step 7

6

Repair the short to power on the terminals as necessary.

Did you complete the repair?

--

System OK

--

7
  1. Replace the TCM. Refer to Transmission Control Module Replacement.
  2. Turn the ignition OFF.
  3. Turn the ignition ON.
  4. Check if DTC P1779 is set.

Is the DTC set?

--

Go to Step 8

Go to Step 9

8

Replace the ECM.

Did you complete the replacement?

--

Go to Step 9

--

9
  1. After the repair, use a scan tool clear info function and road test the vehicle.
  2. Review the DTC info.

Has the last test failed or is the current DTC displayed?

--

Go to Step 1

System OK