GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Sonoma Pickup - 2WD 🢒 Body and Accessories 🢒 Data Link Communications 🢒 DTC C0308

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, AUTO 4WD, 2H, N, and 4L ranges.

This DTC detects a short to ground in Motor Control A or Motor Control B CKT.

Conditions for Setting the DTC
    • The system will test the motor circuits:
       - First, the system checks for unwanted voltage.
       - Then, the system supplies voltage on one circuit and reads the voltage back on the other.
    • If the system detects a problem with the circuits, the DTC is logged.
    • The transfer case shift control module senses a low voltage return in Motor Control A or Motor Control B when a high voltage is expected.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator will be latched 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 encoder motor operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Tests for a short to ground in the Motor Control A circuit.

    3.

  3. Tests for a short to ground in the Motor Control B circuit.

    4.

  4. Tests for a higher than normal resistance in the Motor Control A and B circuits through the module.

    5.

  5. Tests for a short to ground in the encoder motor windings.

    6.

  6. Tests for continuity across the motor circuit. Resistance readings vary depending on the location of the brush contact inside the motor assembly.

    7.

  7. Tests Motor Control A circuit for a short to ground.

    8.

  8. Tests Motor Control B circuit for a short to ground.

    9.

  9. Tests Motor Control A and B circuits for an open or high resistance.

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. Check and replace the ATC fuse as neccessary.
  2. Install a scan tool.
  3. Start the engine.
  4. With the scan tool, command the Motor A/B control ON and OFF.

Does the 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 4 wire connector at the transfer case.
  3. Connect a DMM between the Motor Control A circuit harness connector and ground at the transfer case connector.

Is the resistance reading less than the specified value?

10 K ohms

Go to Step 8

Go to Step 4

4

Connect a DMM between the Motor Control B circuit harness connector and ground at the transfer case.

Is the resistance reading less than the specified value?

10 K ohms

Go to Step 9

Go to Step 5

5

Connect a DMM between the Motor Control A and B circuit harness connector at the transfer case.

Is the resistance reading greater than the specified value?

2 ohms

Go to Step 6

Go to Step 11

6

Test terminals A and B at the transfer case side of the harness for a short to ground. Refer to Circuit Testing in Wiring Systems.

Was a short to ground found?

--

Go to Step 11

Go to Step 7

7

Test the resistance across the motor circuit.

Was the motor within the specified values?

0.5-35 ohms

Go to Step 10

Go to Step 11

8

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

Was the condition found and corrected?

--

Go to Step 13

Go to Step 12

9

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

Was the condition found and corrected?

--

Go to Step 13

Go to Step 12

10

  1. Disconnect the transfer case shift control module.
  2. Test the Motor Control A and B circuits for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 13

Go to Step 12

11

Replace the encoder motor. Refer to Transfer Case Motor/Encoder Replacement .

Is the repair complete?

--

Go to Step 13

--

12

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

Is the repair complete?

--

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK