C0321
DTC C0321
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 Descriptors
DTC C0321 01
- Transfer Case Module Lock Circuit Short to Battery
DTC C0321 02
- Transfer Case Module Lock Circuit Short to Ground
DTC C0321 04
- Transfer Case Module Lock Circuit Open
DTC C0321 08
- Transfer Case Module Lock Circuit Signal Invalid
Diagnostic Fault Information
Circuit/System Description
The transfer case shift control module (TCCM) controls the transfer case actuator lock solenoid. The transfer case actuator lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during range changes, and 4WD Auto mode. Locking action is applied when power or ground are taken away from the lock solenoid, preventing the transfer case encoder motor (TCEM) from moving. The system is capable of providing a 2WD HI, 4WD HI and 4WD LO lock-up without the need of additional vehicle power to hold the transfer case in these positions.
Conditions for Running the DTC
* Ignition ON.
* System voltage 10.5-18 V.
Conditions for Setting the DTC
* The system tests the lock solenoid circuits by checking for unwanted voltage.
* The underhood fuse block supplies B+ on the battery positive voltage circuit and reads the voltage back on the lock solenoid control circuit.
* If the TCCM detects a low voltage return when a high voltage is expected, or a high voltage return when a low voltage is expected, the DTC is logged.
* The fault must remain current for 1 second to set the DTC.
Action Taken When the DTC Sets
C0321 01 and C0321 04
* Shifts allowed. Clutch engages only if slip is detected.
* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
C0321 02 and C0321 08
* Normal operation.
* The SERVICE 4WD indicator remains 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 clears after 40 consecutive warm up cycles without a fault present.
* History DTCs can be cleared using a scan tool.
Diagnostic Aids
* 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 (MP 3023/3024-NQH - Transfer Case)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Control Module References) for scan tool information.
Special Tools
* EL-49741 - 9 V+ Power Source Harness
* EL-49742 - Battery Voltage B+ and Ground Source Harness
* J 35616 - GM-Approved Terminal Test Kit
Circuit/System Verification
1. Key ON, engine OFF.
2. Connect a scan tool.
3. Parking brake engaged. Transmission in Neutral.
4. Using the Transfer Case Lock function of the Special Function feature of the scan tool, command the transfer case lock ON and OFF. You should be able to hear the encoder motor lock engage and disengage.
Circuit/System Testing
1. Verify that the TREC fuse, and the Miscellaneous IGN fuse, underhood fuse block, are not open.
• If the TREC fuse is open, test the battery positive voltage, TCCM harness X3 pin C, for a short to ground.
• If the Miscellaneous IGN fuse is open, test the Ignition 1 voltage circuit, TCCM harness X2 pin 6, for a short to ground.
2. Ignition ON, engine OFF.
3. 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 - Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.
4. Using the PU probes J 35616-4A, test for B+ (+0.0/-1.0 V) between the battery positive voltage circuit, TCEM harness X1 pin B, and a good ground.
• If the voltage is less than the specified range, test the affected circuit for an open/high resistance or short to ground condition. If all circuits and connections test normal, test the TCCM.
5. Using the PU probe J 35616-4A, test for a 4.0-5.0 V diagnostic voltage between the lock solenoid control circuit, TCEM X1 pin C, and a good ground.
• If the voltage is greater than the specified range, test the affected 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 affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM.
6. Test the TCEM.
Component Testing
Transfer Case Encoder Motor (TCEM) - Actuator Lock, Motor A and Motor B
1. Remove the encoder motor 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. Install EL-49742 - harness.
3. Using a PU probe J-35616-5, attach the red lead from the EL-49742 - jumper harness to the motor control A terminal of the TCEM, pin A.
4. Using a PU probe J-35616-5, touch the black lead from this same jumper harness to the motor control B terminal of the TCEM, pin D. The encoder motor drive gear should not rotate.
• If the encoder motor rotates, replace the encoder motor.
5. Using a PU probe J-35616-5, attach the red lead from the EL-49741 - harness to the battery positive voltage terminal of the TCEM harness, pin B.
6. Using a PU probe J-35616-5, attach the black lead from this same jumper harness to the lock solenoid control terminal of the TCEM harness, pin C.
7. Attach a 9-volt battery to this harness (not included). You should hear the encoder motor unlock.
• If you do not hear the TCEM unlock, test the affected circuits of the TCEM harness for an open/high resistance, short to ground or short together. If all circuits and connections test normal, replace the TCEM.
8. Touch the black lead from EL-49742 - jumper harness to the motor control B terminal of the TCEM, pin D. The encoder motor drive gear should rotate.
• If the encoder motor drive gear does not rotate, replace the encoder motor.
9. Using the PU probes J 35616-5, test for between 10-30 ohm between the battery positive voltage circuit TCEM, pin B and the lock solenoid control circuit TCEM pin C.
• If outside the specified range, replace the encoder motor.
10. Using the PU probes J 35616-5, test for greater than 1 M ohm between the following circuits and the encoder motor case:
* Battery positive voltage circuit TCEM, pin B.
* Lock solenoid control circuit TCEM pin C.
• If less than the specified value, replace the encoder motor.
11. Using the PU probes J 35616-5, test for greater than 1 M ohm between the battery positive voltage circuit TCEM, pin B and all other pins on the TCEM X1 except the lock solenoid control circuit TCEM, pin C.
• If less than the specified value, replace the encoder motor.
12. Using the PU probes J 35616-5, test for greater than 1 M ohm between the lock solenoid control circuit TCEM, pin C and all other pins on the TCEM X1 except the battery positive voltage circuit TCEM, pin B.
• If less than the specified value, replace the encoder motor.
13. Test the TCCM.
TCCM
Note: TCCM's need to be programmed when replaced. If after programming the TCCM comes back as "NO COMM", try reprogramming again. (Internet/vehicle bandwidth load may cause the programming activity to fail.)
1. Ignition OFF. Disconnect the X1 harness connector at the TCEM.
2. Ignition ON, engine OFF. Install EL-49742 - harness.
3. Block wheels. Parking brake engaged. Transmission in Neutral.
4. Using the PU probes J 35616-4A, connect a test lamp between the battery positive voltage circuit, TCEM X1 pin B and the ground terminal of EL-49742 - harness , black terminal. The test light should illuminate.
• If the test light does not illuminate, test the battery positive voltage circuit for an open or short to ground. If all circuits and connections test normal, reprogram the TCCM. If the DTC continues to set replace the TCCM.
5. Using the PU probes J 35616-4A, connect a test lamp between the battery positive voltage circuit, TCEM X1 pin B and the lock solenoid control circuit, TCEM X1 pin C. The test light should not illuminate.
• If the test light illuminates, test the lock solenoid control circuit for a short to ground. If all circuits and connections test normal, reprogram the TCCM. If the DTC continues to set replace the TCCM.
6. Using the Transfer Case Lock function of the Special Function feature of the scan tool, command the transfer case lock ON and OFF. When the lock is commanded ON, release solenoid de-energized, the test light should not illuminate. When the lock is commanded OFF, release solenoid energized, the test light should illuminate.
• If the test light stays ON when the lock is commanded ON, test the lock solenoid control circuit for a short to ground. If all circuits and connections test normal, reprogram the TCCM. If the DTC continues to set replace the TCCM.
• If the test light does not illuminate when the lock is commanded OFF, test the lock control solenoid circuit for an open or short to voltage. If all circuits and connections test normal, reprogram the TCCM. If the DTC continues to set replace the TCCM.
7. Test the TCEM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Control Module References (Control Module References) for TCSCM replacement, setup, and programming
* Transfer Case High/Low Clutch Reset (Transfer Case High/Low Clutch Reset)
* Transfer Case Two/Four Wheel Drive Actuator Position Sensor Replacement (Transfer Case Two/Four Wheel Drive Actuator Position Sensor Replacement)
* Transfer Case Disassemble (Transfer Case Disassemble)
* Transfer Case Assemble (Transfer Case Assemble)
* Oil Pump Cleaning and Inspection (Oil Pump Cleaning and Inspection)
* Rear Output Shaft Cleaning and Inspection (Rear Output Shaft Cleaning and Inspection)
* Front Output Shaft and Input Shaft Cleaning and Inspection (Front Output Shaft and Input Shaft Cleaning and Inspection)
* Drive Chain, Drive Sprocket, and Driven Sprocket Cleaning and Inspection (Drive Chain, Drive Sprocket, and Driven Sprocket Cleaning and Inspection)
* High/Low Planetary Carrier Cleaning and Inspection (High/Low Planetary Carrier Cleaning and Inspection)
* High/Low Shift Components Cleaning and Inspection (High/Low Shift Components Cleaning and Inspection)
* Two/Four Wheel Drive Shift Components Cleaning and Inspection (Two/Four Wheel Drive Shift Components Cleaning and Inspection)
* Transfer Case Front Half Cleaning and Inspection (Transfer Case Front Half Cleaning and Inspection)
* Transfer Case Rear Half Cleaning and Inspection (Transfer Case Rear Half Cleaning and Inspection)