GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Epica 🢒 DTC 🢒 DTC P1780

Circuit Description

The transaxle control module (TCM) is an electronic device which monitors inputs to control various transaxle functions, including shift quality and transaxle senors, 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.

The following information transmits between the TCM and engine control module (ECM):

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

Conditions for Setting the DTC
    • The engine speed is greater than 7,000 RPM.
    • 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.
    • Adopt Emergency/Substitute mode and constant 4th gear.
    • Open lock up clutch

Conditions for Clearing the DTC

Using a scan tool can clear history DTCs.

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

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Automatic Transmission?

--

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Record, then clear the DTCs.
  4. Turn the ignition OFF.
  5. Observe the engine speed on the scan tool.

Is the speed within the specified values?

0-7,000 RPM

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the transaxle control module (TCM) wiring connector and the engine control module (ECM) wiring connector.
  3. Measure the resistance between terminal A13 of the TCM wiring connector, and terminal B12 of the ECM wiring connector.

Is the resistance within the specified values?

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 ON the ignition, with the engine OFF.
  2. Measure the voltage of terminal A13.

Is the voltage within the specified values?

11-14 V

Go to Step 6

Go to Step 7

6

Repair the short to power.

Did you complete the repair?

--

System OK

--

7

Inspect the engine speed. Refer to Diagnostic System Check - Engine Controls in Engine Controls-2.0L.

Was a condition found?

--

Verify Repair

Go to Step 8

8
  1. Replace the TCM. Refer to Transmission Control Module Replacement .
  2. Turn the ignition OFF.
  3. Turn ON the ignition, with the engine OFF.
  4. Ensure that DTC P1780 is set.

Is DTC P1780 set?

--

Go to Step 9

Go to Step 10

9

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls-2.0L.

Did you complete the replacement?

--

Go to Step 10

--

10
  1. Clear the DTCs with a scan tool.
  2. Road test the vehicle.
  3. Observe the DTC information with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Step 2

System OK