GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Holden 🢒 2005 🢒 Calais 🢒 DTC 🢒 DTC P0785

DTC Description

This diagnostic procedure covers DTC P0785 -- 3-2 Downshift Control Solenoid Circuit Fault.

Circuit Description

The 3-2 Shift Solenoid controls the normally closed, 3-port, 3- downshift valve. The solenoid attaches to the control valve body within the transmission. The solenoid receives ignition voltage through circuit 339. The powertrain control module (PCM) controls the solenoid by providing a ground path on circuit 898. During a 3-2 downshift, the 2-4 band applies as the 3-4 clutch releases. The PCM varies the timing between the 3-4 clutch release and the 2-4 band apply depending on the vehicle speed and the throttle position.

When the PCM detects a fault in the 3-2 shift solenoid circuit 3-2 downshift control solenoid circuit DTC sets.

Conditions for Running the DTC
    • The system voltage is between 8.0-18.0 volts.
    • The engine speed is greater than 300 RPM for 5 seconds.
    • The engine is not in fuel cut-off.

Conditions for Setting the DTC
    • The PCM commands the solenoid ON and the voltage input remains high (12 volts).
        OR
    • The PCM commands the solenoid OFF and the voltage input remains low (0 volts).

Conditions for Clearing the DTC

The 3-2 shift solenoid DTC is a Type B DTC. Refer to Diagnostic Starting Point - Automatic Transmission for Action Taken when Type B DTCs set and Conditions for Clearing Type B DTCs.

Additional Information
    • Verify that the transmission shift pattern complies with the shift pattern charts. Refer to Functional Test. Other internal transmission failures may cause more than one shift to occur.
    • Refer to Transmission General Information for details of the 3-2 shift solenoid operation.
    • For an intermittent fault condition, refer to Intermittent Conditions.
    • Since a fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic procedure for shorted terminals or poor wiring connections before replacing any component. Refer to Testing for Intermittent Conditions and Poor Connections for information on electrical fault diagnosis.
    • Refer to Automatic Transmission Controls Schematics , Automatic Transmission Inline 20-Way Connector End View , Automatic Transmission Internal Connector End Views , Automatic Transmission Control Module Connector End Views , and Automatic Transmission Related Connector End Views to aid in the diagnosis procedures.

Test Description

The following number refers to the step number on the diagnostic chart.

7 This diagnostic table only tests the 3-2 shift solenoid circuits outside the transmission. Check for damaged wiring or poor connections inside the transmission assembly before replacing the 3-2 shift solenoid. Measure the resistance of the 3-2 shift solenoid. Refer to Transmission General Specifications.

Step

Action

Yes

No

1

Was the Main Diagnostic Table performed?

Go to Step 2

Refer to Diagnostic System Check - Automatic Transmission

2
  1. Using Tech 2, observe the Freeze Frame/Failure Records for this DTC.
  2. Switch OFF the ignition for 30 seconds
  3. Operate the vehicle within the Conditions for Running the DTC or within the conditions in the Freeze Frame/Failure Records.
  4. Using Tech 2 select Engine/Diagnostic Trouble Codes/Read DTC Information.

Does DTC P0785 fail this ignition cycle?

Go to Step 3

Refer to Diagnostic Aids for the 3-2 Shift Solenoid DTCs

3
  1. Switch ON the ignition with the engine not running.
  2. Connect a test lamp between the 3-2 shift solenoid ignition voltage circuit and a known ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4
  1. Switch OFF the ignition.
  2. Disconnect connector X121-X2 from the transmission assembly.
  3. Switch ON the ignition with the engine not running.
  4. Using Tech 2, command the 3-2 shift solenoid ON and OFF.
  5. Connect a test lamp between the 3-2 shift solenoid ignition voltage circuit and the 3-2 shift solenoid control circuit.

Does the test lamp illuminate ON and OFF when the 3-2 shift solenoid is commanded ON and OFF?

Go to Step 7

Go to Step 5

5

Test the 3-2 shift solenoid control circuit for an open circuit, short to ground, high resistance, or short to voltage fault condition. Refer to Testing for Intermittent Conditions and Poor Connections for information on electrical fault diagnosis.

Was any fault found and rectified?

Go to Step 9

Go to Step 8

6

Repair the open circuit, short to ground, high resistance, or short to voltage fault condition in the 3-2 shift solenoid ignition voltage circuit. Refer to Wiring Repairs for information on electrical wiring repair procedures.

Was the repair completed?

Go to Step 9

--

7

Important: Check for damaged wiring (short to ground, short to voltage, high resistance, or open circuit) or poor connections inside the transmission assembly before replacing the 3-2 shift solenoid.

Replace the 3-2 shift solenoid. Refer to 2-3 Shift Solenoid Valve Replacement.

Was the repair completed?

Go to Step 9

--

8

Replace the PCM. Refer to Powertrain Control Module Replacement.

Was the repair completed?

Go to Step 9

--

9
  1. Using Tech 2, clear the DTCs.
  2. Switch OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC or within the conditions in the Freeze Frame/Failure Records.

Do any 3-2 shift solenoid DTCs fail this ignition cycle?

Go to Step 2

Go to Step 10

10

Using Tech 2, select the DTC Display function.

Are there any DTCs displayed?

Refer to Diagnostic Trouble Code (DTC) List/Type

System OK

When all diagnosis and repairs are completed, check the powertrain management system for correct operation.