GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Astro - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 136-NP4 🢒 DTC C0309

Circuit Description

The transfer case encoder motor is a permanent magnet DC motor and gear reduction assembly. The encoder motor is controlled with a pulse width modulated (PWM) circuit within the transfer case shift control module. This circuit consists of a power supply relay (Motor Control A) circuit that supplies voltage to the motor. The Motor Control B circuit is a PWM driver that varies the duty cycle to control the amount of current through the motor to ground.

This DTC detects a short to power on the Motor Control A circuit or the Motor Control B circuit.

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

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

Action Taken When the DTC Sets
    • The SERVICE (AWD) indicator will remain illuminated for the remainder of the current ignition cycle.
    • All clutch activation, slip control will be disabled.

Conditions for Clearing the DTC
    • Current 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. Tests Motor Control A for an open or short to voltage.

    2.

  2. Tests Motor Control B for an open or short to voltage.

    3.

  3. Tests for continuity across the motor windings.

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

  1. Turn OFF the ignition.
  2. Disconnect the encoder motor.
  3. Disconnect the transfer case shift control module.
  4. Turn ON the ignition, with the engine OFF.
  5. Test Motor Control A for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 7

Go to Step 3

3

Test Motor Control B for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find an correct the condition?

Go to Step 7

Go to Step 4

4

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

Did you find there was continuity?

Go to Step 6

Go to Step 5

5

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

Did you complete the repair?

Go to Step 7

--

6

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

Did you complete the repair?

Go to Step 7

--

7
  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