GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 126-NP4 🢒 DTC C0374

Circuit Description

The transfer case shift control module senses rear slip. After several attempts of applying torque to the front wheels by activating the encoder motor, the transfer case still sees a difference in speed between the front propshaft speed sensor and rear propshaft speed sensor.

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 9-18 volts.

Conditions for Setting the DTC

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

Action Taken When the DTC Sets
    • All shifts to Auto mode are disabled. If the current mode is Auto, the system does not allow any further adaptive events, such as correcting slip.
    • The SERVICE AWD 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 determines if the rear propshaft speed sensor and wiring are operating properly.

    2.

  2. This step determines if the front propshaft speed sensor and wiring are operating properly.

    3.

  3. This step determines if the motor control A or motor control B circuits are shorted to ground within the encoder motor.

    4.

  4. This step tests the integrity of the motor windings.

    5.

  5. This step tests the motor control A and motor control B circuits for an open, short to ground, or high resistance between the encoder motor and the transfer case shift control module.

    6.

  6. This step determines whether the transfer case is mechanically functioning properly.

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 - Transfer Case?

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Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Take the vehicle on a short test drive.
  2. With the scan tool, observe the Rear Propshaft Speed Data Parameter in the Transfer Case Data List while driving.

Does the RPM value vary or become intermittent while driving?

--

Go to DTC C0300

Go to Step 3

3

  1. Take the vehicle on a short test drive.
  2. With the scan tool, observe the Front Propshaft Speed Data Parameter in the Transfer Case Data List while driving.

Does the RPM value vary or become intermittent while driving?

--

Go to DTC C0305

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the encoder motor connector.
  3. With a DMM at the encoder motor pigtail connector, test motor control A and motor control B for a short to ground within the encoder motor.

Is motor control A or motor control B shorted to ground?

--

Go to Step 9

Go to Step 5

5

Important: Use test leads designed for this connector and make firm contact with the leads.

  1. Turn OFF the ignition.
  2. Zero the DMM with Ohms selected, by touching the two leads.
  3. Connect the DMM between motor control A terminal and motor control B terminal and test the resistance in the encoder motor.

Is the encoder motor within the specified values?

0.3-35 ohms

Go to Step 6

Go to Step 9

6

Test the motor A and motor B control circuits for a short to ground, short to voltage, open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 7

7

  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 pry bar between the front propshaft U-joint.

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

--

Go to Step 9

Go to Step 8

8

Remove the transfer case and overhaul. Refer to Transfer Case Disassemble in Transfer Case - NVG 126 Unit Repair.

Did you complete the repair?

--

Go to Step 11

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9

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

Did you complete the repair?

--

Go to Step 11

--

10

Important: After transfer case shift control module replacement and reprogramming , ensure all doors are closed and the key is out of the ignition, then open and close the doors again and wait 2 minutes to avoid incomplete programming or false communication DTCs.

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

Did you complete the repair?

--

Go to Step 2

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11
  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 10

System OK