GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H2 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C0306

Circuit Description

The transfer case motor is a bi-directional, permanent magnet, D.C. motor. When energized, through motor control A or motor control B, the ground is provided by the opposing motor control circuit and 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 the following ranges:

    • 4HI
    • 4HI Lock
    • 4LO Lock
    • Neutral

This DTC detects an open, short to voltage, or short to ground in the motor control A or motor control B circuits, or an open, or short to ground inside the motor.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0306 Motor A or B Circuit Malfunction

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

Conditions for Setting the DTC
    • The system will test the motor circuits by checking for unwanted voltage.
    • Then, the system supplies voltage on each of the motor circuits and reads the voltage back on the other circuit.
    • If the system detects a problem with the circuits, the DTC is logged. The transfer case shift control module senses a low voltage return in the motor control A or motor control B circuits when a high voltage is expected.
    • The fault must remain current for 1.2 seconds to set the DTC.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator will remain illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
    • 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. This step tests motor A driver high for proper operation.

    2.

  2. This step tests motor B driver high for proper operation.

    3.

  3. This step tests motor A driver low for proper operation.

    4.

  4. This step tests motor B driver low for proper operation.

    5.

  5. This step tests motor control A and motor control B circuits for being shorted together.

    6.

  6. This step tests motor control A for a short to ground, short to voltage, open, or high resistance.

    7.

  7. This step tests motor control B for a short to ground, short to voltage, 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

2

  1. Engage the parking brake.
  2. Turn the ignition OFF and raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle .
  3. Disconnect the motor encoder connector at the transfer case.
  4. Turn the ignition ON.
  5. With a digital multimeter (DMM), measure voltage by probing the motor control A circuit and take the other lead to a good ground.
  6. With a scan tool, command motor A driver high ON.

Does the DMM indicate battery voltage?

--

Go to Step 3

Go to Step 7

3

  1. With a DMM, measure voltage by probing the motor control B circuit and take the other lead to a good ground.
  2. With a scan tool, command motor B driver high ON.

Does the DMM indicate battery voltage?

--

Go to Step 4

Go to Step 8

4

  1. With a DMM, measure voltage by probing the motor control A circuit and take the other lead to ground.
  2. With a scan tool, command motor A driver low ON.

Does the voltage on the DMM match the voltage indicated?

0 V

Go to Step 5

Go to Step 7

5

  1. With a DMM, measure voltage by probing the motor control B circuit and use the other lead to probe one of the four encoder signal circuits.
  2. With a scan tool, command motor B driver low ON.

Does the DMM indicate voltage within the specified range?

4.3-4.7 V

Go to Step 6

Go to Step 8

6

With a DMM, check motor control A and motor control B circuits for being shorted together.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

7

With a DMM, check the motor control A circuit for a short to ground, short to voltage, open, or high resistance.

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

8

With a DMM, check the motor control B circuit for a short to ground, short to voltage, open, or high resistance.

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

9

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

Did you complete the repair?

--

Go to Step 11

--

10

Replace the transfer case shift control module. Refer to Control Module References for replacement, setup and programming.

Did you complete the repair?

--

Go to Step 11

--

11
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK