GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Shift D solenoid is a normally closed (N/C) solenoid that provides control main pressure to stroke the D shift valve. The transmission control module (TCM) determines the proper solenoid command logic to move the D shift valve to attain a particular range.

Since the valve state, stroked or unstroked, is critical to providing the correct transmission range, the shift valve has a pressure switch, located in the pressure switch manifold, to provide feedback to the TCM as to the position of the valve.

DTC P0768 is a type A DTC.

Conditions for Running the DTC

    • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
    • TCM initialization is in process or engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.

Conditions for Setting the DTC

DTC P0768 sets when the TCM detects one of the following conditions for greater than 100 milliseconds:

    • An open circuit or short to ground is detected when D solenoid is commanded OFF.
    • A short to power is detected when D solenoid is commanded ON.

Action Taken When the DTC Sets

    • The TCM illuminates the malfunction indicator lamp (MIL).
    • When in a forward range, the transmission will shift to another forward range while diagnostic response is active.
    • If the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL.
    • If the shift selector is moved to REVERSE, the transmission will shift to NEUTRAL or REVERSE.
    • If the shift selector is returned to a forward range and the transmission is compromised by over speeding or direction change, the transmission will lock in NEUTRAL.
    • DTC P0768 will be stored in TCM history.
    • The TCM freezes shift adapts (DNA).
    • The TCM inhibits torque converter clutch (TCC) engagement.

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids

    • Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
       - A bent terminal
       - A backed-out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • You may have to drive the vehicle in order to experience a condition.
    • Solenoids are sensitive to battery voltage spikes and poor ground connections. This condition may not be indicated with your scan tool, or with a DMM.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests ignition voltage.

  2. This step tests the command signal from the TCM.

  3. This step tests the resistance value of the external harness and solenoid.

  4. This step tests the resistance value of the solenoid, and internal wiring harness.

  5. This step tests the resistance value of the solenoid.

Step

Action

Value

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Automatic Transmission?

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Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

2

  1. Install the scan tool.
  2. Start the engine.
  3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  4. Record the DTC Freeze Frame and Failure Records.
  5. Clear the DTC.
  6. Using the scan tool, measure ignition voltage.

Is the voltage within the specified range?

9-18 V

Go to Step 3

Go to DTC P0562 for low voltage or DTC P0563 for high voltage

3

  1. Turn the ignition OFF.
  2. Disconnect the C2 connector (RED) at the TCM.
  3. Install the J 39700 breakout box and the J 43799 breakout box adapter.
  4. Using a DMM, measure voltage between connector C2 terminal 27 and terminal 31.
  5. Turn ON the ignition, with the engine OFF.
  6. Using the scan tool, command D solenoid to ON.

Is voltage within the range specified when D solenoid is commanded ON?

B+

Go to Step 4

Go to Step 10

4

  1. Turn the ignition OFF.
  2. Using a DMM, measure the resistance between connector C2 terminal 27 and terminal 31.

Is the resistance reading within the specified range?

22.0 ohms @ 20°C (68°F)

Go to Diagnostic Aids

Go to Step 5

5

  1. Turn the ignition OFF.
  2. Connect the C2 connector (RED) at the TCM.
  3. Disconnect the wiring harness from the transmission 20-way connector.
  4. Using a DMM, measure resistance on the transmission side of the 20-way connector between terminals B and C.

Is resistance within the specified range ?

22.0 ohms @ 20°C (68°F)

Go to Step 6

Go to Step 7

6

Inspect the engine wiring harness circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 11

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7

  1. Remove the oil pan. Refer to Oil Pan Replacement .
  2. Remove the AT internal wiring harness at D solenoid connector.
  3. Using a DMM, measure the resistance of D solenoid.

Is the solenoid resistance within the specified value?

22.0 ohms @ 20°C (68°F)

Go to Step 8

Go to Step 9

8

Replace the AT internal wiring harness. Refer to Wiring Harness Replacement .

Did you complete the replacement?

--

Go to Step 11

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9

Replace D solenoid. Refer to Control Valve Solenoid Replacement .

Did you complete the replacement?

--

Go to Step 11

--

10

Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Transmission Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

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11

Perform the following procedure in order to verify the repair:

  1. Clear the DTC.
  2. Drive the vehicle under normal operating conditions.
  3. Select Specific DTC.
  4. Enter DTC P0768.

Has the test run and passed?

--

System OK

Go to Step 1