GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 4WD 🢒 Restraints 🢒 SIR 🢒 DTC C0308

Circuit Description

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized through motor control A or motor control B, the ground is provided by the opposing motor control circuit, 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 circuit.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0308 Motor A/B Circuit Low

Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is 9-16 volts.

Conditions for Setting the DTC
    • The system tests 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 condition 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 is disabled.
    • The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module clears the DTC if the condition for setting the DTC no longer exists.
    • A history DTC clears 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. This step listens for an audible motor noise when the encoder motor operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. This step tests for a short to ground in the motor control A circuit.

    3.

  3. This step tests for a short to ground in the motor control B circuit.

    4.

  4. This step tests for a higher than normal resistance in the motor control A and B circuits through the module.

    5.

  5. This step tests for a short to ground in the encoder motor windings.

    6.

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

    7.

  7. This step tests motor control A circuit for a short to ground.

    8.

  8. This step tests motor control B circuit for a short to ground.

    9.

  9. This step 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

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Inspect and replace the ATC fuse as necessary.
  2. Install a scan tool.
  3. Start the engine.
  4. Using a 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 terminal A and B at the transfer case side of the harness for a short to ground. Refer to Testing for Short to Ground in Wiring Systems.

Was a short to ground found?

--

Go to Step 11

Go to Step 7

7

Test for continuity across the motor circuit. Refer to Testing for Continuity in Wiring Systems.

Was the motor within the specified range?

0.8-35 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 Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

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 Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

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 Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

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

Did you complete the repair?

--

Go to Step 13

--

12

Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the repair?

--

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 set?

--

Go to Step 2

System OK