GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Astro - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 136-NP4 🢒 DTC C0374

Circuit Description

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

Conditions for Running the DTC
    • 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 clutch activation, slip control will be disabled.
    • The Service AWD indicator will remain illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • A history DTC will clear 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. Determines of DTCs C0300 or C0305 have set.

    2.

  2. Helps determine if the DTC set due to a mechanical or an electrical fault.

    3.

  3. Tests the integrity of the Motor Control circuit.

    4.

  4. Determines whether the transfer case clutch pack is holding.

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Did you perform the Diagnostic System Check - Transfer Case?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Has the transfer case shift control module set DTC C0300 or C0305 as a current DTC, or does the front or rear propshaft RPM drop out or become erratic while driving at a constant and steady speed?

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. Use the scan tool in order to command the Encoder Motor B ON.

Is the motor encoder turning ON?

Go to Step 5

Go to Step 4

4

  1. Turn the ignition OFF.
  2. Disconnect the encoder motor harness.
  3. Turn the ignition ON, with the engine OFF.
  4. Use the scan tool to check for DTCs.

Did DTC C0310 set?

Go to Step 7

Go to Step 8

5

  1. Remove the encoder motor assembly. Refer to Transfer Case Motor/Encoder Replacement .
  2. Connect a wrench to the transfer case sector shaft.
  3. Turn the sector shaft to apply the clutch pack.
  4. While the clutch pack is applied, attempt to turn the front propshaft using a small pry bar between the U-Joint.

Does the clutch pack hold the propshaft and prevent it from being turned?

Go to Step 7

Go to Step 6

6

Remove the transfer case and overhaul.

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 reset?

Go to Step 2

System OK