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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 to the motor control B circuit and reading the return voltage back on the motor control A circuit.

Conditions for Running the DTC

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

Conditions for Setting the DTC

* The TCCM tests the motor circuits by checking for unexpected voltage.
* The TCCM supplies voltage on each of the motor circuits and reads the voltage back on the other circuit.
* 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 disabled.
* The SERVICE 4WD indicator will remain illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

* The TCCM clears the DTC once the conditions for setting the DTC are no longer 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 shorted to the case, resulting in a short to ground, causing this DTC to set.
* The default actions for C0321 may set C0306.
* EL-49741 - harness is a good source for 9 V.
* EL-49742 - harness is a good source for B+ and ground.
* The transfer case drain plug is a good source for ground.

Reference Information
Schematic Reference

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

Component Connector End Views (Connector End Views By Name)
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. Verify that DTC C0327 is not set. If DTC C0327 is set, go to C0327.
3. Ignition ON. Engine OFF
4. Disconnect the X1 harness connector at the transfer case encoder motor (TCEM).
Note: 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.

5. Using the PU probe J 35616-4A, test for a 2.8-4.0 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, test 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, test the TCCM.

6. Using the PU probes J 35616-4A, test for 2.8-4.0 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, test 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, test the TCCM.

Note: When removing the transfer case encoder motor, the transfer case will try to move into the neutral position.

7. Remove the encoder motor from transfer case. Refer to Transfer Case Motor/Encoder Replacement (Service and Repair). Using a paint pen or marker, place indexing marks on the encoder motor drive gear and the mounting surface of the encoder motor.
8. Connect the X1 connector at the transfer case encoder motor (TCEM). Position the TCEM so that the indexing marks are visible from the side of the vehicle.
9. Remove key. Wait 30 seconds. Key ON, engine OFF.
10. With a scan tool, clear codes. Recheck DTC's. If DTC C0327 is set, go to C0327.
11. Block wheels. Parking brake engaged. Transmission in Neutral.
12. Using the transfer case shift control switch (TCSCS), also known as the accessory or multifunction I/P switch, attempt to shift the transfer case to a different mode.

• If the encoder motor is unable to make the shift, test the TCEM.

13. Inspect the transfer case shift cam and shaft assembly for a binding condition. If binding, remove the transfer case and repair the binding condition.
14. If all circuits and connections test normal, test the TCEM.

Component Testing

TCEM (Transfer Case Encoder Motor) - Motor A and Motor B

Note: When removing the transfer case encoder motor, the transfer case will try to move into the neutral position.

1. Remove the TCEM from transfer case. Using a paint pen or marker, place indexing marks on the encoder motor drive gear and the mounting surface of the encoder motor.
2. Using a PU probe J-35616-5, attach the red lead from the EL-49741 - jumper harness to the motor control A terminal of the TCEM, pin E.
3. Using a PU probe J-35616-5, attach the black lead from this same jumper harness to the motor control B terminal of the TCEM, pin D.
4. Touch the battery terminals of the 9-volt battery to the battery terminals of the jumper harness. This should rotate the encoder motor drive socket in either a clockwise or counterclockwise rotation depending on battery orientation.

• If the encoder motor drive socket does not rotate, replace the encoder motor.

5. Using the PU probes J 35616-5, test for between 0.3-40 ohm between the motor control A circuit TCEM X1 pin E and the motor control B circuit TCEM X1 pin D.

• If greater than the specified range, replace the encoder motor.
• If less than the specified range, replace the encoder motor.

6. Using the PU probes J 35616-5, test for greater than 1 M ohm between the following circuits and the encoder motor case:

* Motor control A, TCEM harness X1 pin E.
* Motor control B, TCEM harness X1 pin D.

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

7. Using the PU probes J 35616-5, test for greater than 1 M ohm between the motor control A circuit, TCEM X1 pin E and all other pins on the TCEM harness X1 except the motor control B, TCEM X1 pin D.

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

8. Using the PU probes J 35616-5, test for greater than 1 M ohm between the motor control B circuit, TCEM X1 pin D. and all other pins on the TCEM harness X1 except the motor control A circuit, TCEM X1 pin E.

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

9. Using the EL-49741 - jumper harness, return the TCEM to the marked position of step 1.
10. Test the TCCM.

TCCM
1. Ignition OFF. Disconnect the X1 harness connector at the TCEM.
2. Ignition ON, engine OFF. Install EL-49742 - harness.
3. Using the PU probes J 35616-4A, connect a test lamp between the motor control A circuit, TCEM X1 pin E and the ground terminal of EL-49742 - harness, black terminal.
4. Using the Motor A Driver (High) function of the Special Function feature of the scan tool, command the Motor A Driver (High) ON and OFF. When commanded ON, the test light should illuminate. When commanded OFF, the test light should turn OFF.

• If the test light stays ON when commanded OFF, test the motor control A circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the test light does not illuminate when commanded ON, test the motor control A circuit for an open or short to ground. If all circuits and connections test normal, replace the TCCM.

5. Using the PU probes J 35616-4A, connect a test lamp between the motor control B circuit, TCEM X1 pin D and the ground terminal of EL-49742 - harness, black terminal.
6. Using the Motor B Driver (High) function of the Special Function feature of the scan tool, command the Motor B Driver (High) ON and OFF. When commanded forward, the test light should turn OFF. When commanded reverse, the test light should illuminate for 10 seconds and turn OFF.

• If the test light stays ON when commanded OFF, test the motor control B circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the test light does not illuminate when commanded ON, test the motor control B circuit for an open or short to ground. If all circuits and connections test normal, replace the TCCM.

7. Using the PU probes J 35616-4A, connect a test lamp between the motor control A circuit, TCEM X1 pin E and the B+ terminal of EL-49742 - harness, red terminal.
8. Using the Motor A Driver (Low) function of the Special Function feature of the scan tool, command the Motor A Driver (Low) ON and OFF. When commanded ON, the test light should illuminate. When commanded OFF, the test light should turn OFF.

• If the test light stays ON when commanded OFF, test the motor control A circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the test light does not illuminate when commanded ON, test the motor control A circuit for an open or short to ground. If all circuits and connections test normal, replace the TCCM.

9. Using the PU probes J 35616-4A, connect a test lamp between the motor control B circuit, TCEM X1 pin D and the B+ terminal of EL-49742 - harness, red terminal.
10. Using the Motor B Driver (Low) function of the Special Function feature of the scan tool, command the Motor B Driver (Low) ON and OFF. When commanded ON, the test light should illuminate. When commanded OFF, the test light should turn OFF.

• If the test light stays ON when commanded OFF, test the motor control B circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the test light does not illuminate when commanded ON, test the motor control B circuit for an open or short to ground. If all circuits and connections test normal, replace the TCCM.

11. Test the TCEM.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests)

* Control Module References (Programming and Relearning) for TCSCM replacement, setup, and programming
* Transfer Case Motor/Encoder Replacement (Service and Repair)
* Transfer Case Disassemble (Transfer Case Disassemble)
* Transfer Case Assemble (Transfer Case Assemble)
* Transfer Case Cleaning and Inspection (Transfer Case Cleaning and Inspection)

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