GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC C0309

Circuit Description

The transfer case motor is a bi-directional, permanent magnet, D.C. motor. When energized, (through Motor Control A or Motor Control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit), the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between 4H, 2H, N, and 4L ranges.

This DTC detects a short to voltage in the motor control A or motor control B circuits, or a shorted motor.

Conditions for Setting the DTC
    • The system will test the motor circuits by reading the voltage on each circuit.
    • If the system detects a problem with the circuits, the DTC is logged.
    • The transfer case shift control module senses a high voltage in the motor control A or motor control B circuits when a low voltage is expected.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator lamp will be commanded on for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module will clear the DTC if the condition for setting the DTC no longer exists.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Test Description

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

  1. Listen for an audible motor noise when the transfer case encoder motor operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step tests motor control A or the transfer case shift control module for a short to voltage.

    3.

  3. This step tests motor control B or the transfer case shift control module for a short to voltage.

    4.

  4. This step tests motor control A circuit for a short to voltage.

    5.

  5. This step tests motor control B circuit for a short to voltage.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Was the Transfer Case Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2
  1. Start the vehicle.
  2. Put the vehicle in NEUTRAL.
  3. Using the transfer case control switches, attempt to shift through all modes and ranges.

Does the transfer case encoder motor turn ON and OFF?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the four wire connector at the transfer case.
  3. Turn the ignition ON, with the engine OFF.
  4. Connect a DMM between the motor control A circuit harness connector and ground at the transfer case.

Is the voltage reading within the specified value?

0-0.2 V

Go to Step 4

Go to Step 5

4

Connect a DMM between the motor control B circuit harness connector and ground at the transfer case.

Does the voltage measure within the specified value?

0-0.2 V

Go to Step 7

Go to Step 6

5
  1. Disconnect the transfer case shift control module.
  2. Test the motor control A circuit harness connector for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6
  1. Disconnect the transfer case shift control module.
  2. Test the motor control B circuit harness connector for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

7

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .

Did you complete the replacement?

--

Go to Step 8

--

8
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK