GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Blazer - 4WD 🢒 DTC 🢒 DTC C0374

Circuit Description

The transfer case shift control module senses rear to front slip, a difference of rear to front wheel speed, and attempts to correct the difference by activating the encoder motor, to apply more torque to the front wheels.

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

Conditions for Setting the DTC

The transfer case shift control module is unable to correct sensed slip for 10 consecutive seconds.

Action Taken When the DTC Sets
    • All shifts to Auto 4WD mode is disabled. If the current mode is Auto 4WD, the system does not allow any further adaptive events, correcting for wheel slip.
    • SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • A history DTC clears after 100 consecutive ignition cycles without a fault present.
    • Use a scan tool in order to clear history and current DTCs.

Test Description

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

  1. This step helps determine if the DTC set due to a mechanical or an electrical fault.

    2.

  2. This step tests the integrity of the motor control circuit.

    3.

  3. This step determines whether the encoder motor is moving to the proper position.

Step

Action

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 - Transfer Case?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Did the transfer case shift control module set DTC C0300 or C0305 as a current DTC?

Go to DTC C0300 or DTC C0305

Go to Step 3

3

  1. Place the transmission in PARK.
  2. Turn the ignition ON, with the engine OFF.
  3. Install a scan tool.
  4. Using the scan tool, command the encoder motor A and B ON.

Is the encoder motor turning ON, or is there a buzzing noise?

Go to Step 5

Go to Step 4

4

  1. Turn the ignition OFF.
  2. Disconnect the encoder motor.
  3. Turn the ignition ON, with the engine OFF.
  4. Cycle the transfer case between 2WD and 4WD.
  5. Use the scan tool to check for DTCs.

Did DTC C0310 set?

Go to Step 7

Go to Step 8

5

  1. Using the scan tool device control for the ATC Mode Switch, manually command the transfer case gear positions.
  2. Use the Increase and Decrease buttons on the scan tool to command through all the ATC Mode Switch states while observing the Encoder Gear Position parameter.

Does the Encoder Gear Position parameter state change as commanded by the scan tool?

Go to Step 6

Go to Step 7

6

Remove the transfer case and overhaul. Refer to Transfer Case Assembly Replacement .

Did you complete the repair?

Go to Step 9

--

7

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

Did you complete the repair?

Go to Step 9

--

8

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

Did you complete the repair?

Go to Step 9

--

9
  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