GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC C0306 02: Motor A or B Circuit Short to Ground

DTC C0306 05: Motor A or B Circuit Short to Battery or Open

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Invalid

Motor A or B Circuit

DTC C0306 02

DTC C0306 05

DTC C0306 05

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Circuit/System Description

The transfer case motor is a bi-directional, permanent magnet, DC 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 modes or ranges:

    • 2HI
    • 4HI
    • 4LO
    • AUTO 4WD
    • 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.

Conditions for Running the DTC

    • The ignition is ON.
    • System voltage is 10.5-18 volts.

Conditions for Setting the DTC

    • The system tests 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 condition 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 30 seconds to set the DTC.

Action Taken When the DTC Sets

    • All shifting is disabled.
    • The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

    • The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
    • A history DTC clears after 40 consecutive warm-up cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Reference Information

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Diagnostic Aids

It is possible to have windings inside the motor shorted to the case resulting in a short to ground causing this DTC to set.

Circuit/System Testing

The motor A control and motor B circuits need to be checked for shorts to ground, opens, high resistance, and shorts to voltage by following the below listed steps.

  1. With the ignition off disconnect connector X3 from the transfer case control module, and also disconnect the connector at the transfer case actuator.
  2. With a DMM check the motor A control and motor B control circuits for an open, high resistance, or short to ground and repair as necessary. If all check good go to the next step
  3. Connect X3 at the transfer case control module and turn on the ignition.
  4. Check to motor A control and motor B control circuits for a short to voltage. If the circuits shows to indication of a short to voltage go to component testing.

Component Testing

  1. Turn the ignition of and check the motor windings for an internal short to ground inside the motor by probing either the motor A control pin and taking the other lead to ground, or the same can be done using motor B control pin. Motor control A is pin A and motor B control is pin D.
  2. If the DMM indicates and short to ground replace the transfer case actuator. If nothing is found continue to the next step.
  3. With a DMM check the resistance of the motor windings by probing pin A and pin D on the transfer case actuator.
  4. The DMM should indicate 0.3-40 ohms, if it does not replace the transfer case actuator and complete the motor learn procedure. If the actuator is within specifications then replace the transfer case control module, program, and complete the motor learn procedure.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References for TCSCM replacement, setup, and programming
    •  Transfer Case High/Low Clutch Reset
    •  Transfer Case Two/Four Wheel Drive Actuator Replacement