C0306

DTC C0306

Diagnostic Instructions

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

DTC Descriptor
DTC C0306
- Motor A or B Circuit Malfunction

Diagnostic Fault Information





Circuit/System 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 which becomes grounded through the transfer case shift control module (TCCM) ground circuit. The motor, through a series of gears, rotates the actuator lever shaft which moves the mode and range forks in order to shift the transfer case between the following modes/ranges:

* 4HI
* 4HI Lock
* 4LO Lock
* Neutral

The TCCM tests both motor circuits for unexpected voltage by suppling a 2.8-4.0 V diagnostic voltage on each of the motor circuits and reading the return voltage back on the other circuit.

Conditions for Running the DTC

* Ignition ON.
* System voltage 11-18 V.

Conditions for Setting the DTC

* If TCCM senses a low voltage return on the motor control A or motor control B circuits when a high voltage is expected.
* The fault must remain current for 1.2 seconds in order 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.

Diagnostic Aids

It is possible to have windings inside the motor short to the case resulting in a short to ground.

Reference Information
Schematic Reference

Transfer Case Control Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Transfer Case Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information.

Circuit/System Testing

1. Verify that the TCCM fuse, fuse 12, underhood fuse block, is NOT open.

• If fuse 12 is OPEN, test the battery positive voltage for a short to ground, TCCM Harness X3 pin B.

2. Ignition ON. Engine OFF
3. Disconnect the X1 harness connector at the transfer case encoder motor (TCEM).
Important: When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 GM terminal test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.


4. Using the purple probe J 35616-4A, test for a 3-4 V diagnostic voltage between the Motor B circuit, TCEM X1 Pin D, and a good ground.

• If the voltage is greater than the specified range, test the Motor B circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the voltage is less than the specified range, test the Motor B circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the TCCM.

5. Using the purple probes J 35616-4A, test for 3-4 V between the Motor B circuit, TCEM harness X1 pin D, and the TCEM Motor A circuit, TCEM harness X1 pin E.

• If the voltage is greater than the specified range, test the Motor A circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the voltage is less than the specified range, test the Motor A circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the TCCM.

6. If all circuits and connections test normal, replace the TCEM.

Component Testing

1. Ignition OFF. Disconnect the X1 harness connector at the TCEM.
2. Using the purple probes J 35616-5, test for 0.3-40 ohms between the motor control A circuit TCEM X1 Pin E and the motor control B circuit TCEM X1 Pin D.

• If outside the specified range, replace the encoder motor.

3. Using the purple probes J 35616-5, test for greater than 10 ohms between the following circuits and a good ground:

* Motor control A circuit, TCEM harness X1 Pin E
* Motor control B circuit, TCEM harness X1 Pin D

• If outside the specified range, replace the encoder motor.


Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.