MP 1625/1626-NQF - Transfer Case
DTC C0387
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 C0387 59
- Unable to Complete Shift Circuit
Diagnostic Fault Information
Circuit/System Description
The transfer case encoder motor (TCEM) 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 (TCCM) ground circuit, the TCEM, through a series of gears, rotates the transfer case control actuator shaft which moves the transfer case two/four wheel drive actuator cam and transfer case high/low shift fork to shift the transfer case between the following modes or ranges:
* 2WD HI
* 4WD HI
* 4WD LO
* Neutral
The transfer case control module monitors actuator current and incremental sensor output in order to shift the transfer case and verify that the proper position has been obtained. Deviations in current and position from expected values will cause this DTC to set.
Conditions for Running the DTC
* Ignition ON.
* System voltage 10.5-18 V.
Conditions for Setting the DTC
A shift request was received but could not be completed within 15 seconds.
Action Taken When the DTC Sets
* All shifting disabled.
* The mode light shall flash upon a requested mode change and then return to the current mode.
* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
* DTC C0569 4B is set.
Conditions for Clearing the DTC
* The TCCM clears the DTC once the conditions for setting the DTC no longer exist.
* 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
* An incomplete shift is one that cannot reach the desired mode or range and cannot return to the original mode or range.
* Intermittent motor control A shorting to motor control B could cause this DTC to set.
* It is possible to have windings inside the motor shorted to the case, resulting in a short to ground, causing this DTC to set.
* If the shift lever detent shaft were to bind, or there was a mechanical failure, or motor A control and motor B control were shorted together, the shift would not be completed. This will cause the DTC to set in order to protect the system components from damage.
* The NQF transfer case uses a detent plunger that can bind, causing the shift shaft not to move. This can be corrected without removing or disassembling the transfer case.
* A faulty transfer case shift control module can cause incorrect incremental sensor or motor current measurements which would also result in this DTC setting.
* 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 fill and drain plugs are a good source for ground.
Reference Information
Schematic Reference
Transfer Case Control Schematics MP 1625/1626-NQF - Transfer Case
Connector End View Reference
Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)
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. 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 circuit, 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.
• If the TREC fuse, and the Miscellaneous IGN fuse are NOT open
2. Ignition ON, engine OFF.
3. With a scan tool, check DTC's. If any other DTC's are set, diagnose them first.
4. Verify DTC P0387 is only set as a history DTC.
• If the DTC is set as current
Refer to Circuit/System Testing.
• If the DTC is set as history
Note: After inspection, apply Nyogel lubricant 760G to each connector terminal. Ensure each connector and CPA is correctly seated.
5. Visually inspect each connector terminal of the automatic transmission 20-way connector and the transmission control module for damage or corrosion. Repair as necessary.
6. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. The DTC should not set.
• If the DTC sets
Refer to Circuit/System Testing.
• If the DTC does not set
7. All OK.
Circuit/System Testing
1. 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-Approved Terminal Test Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.
2. Using the purple probe J 35616-4A, test for a 1.0-2.5 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.
3. Using the purple probes J 35616-4A, test for a diagnostic B+ (+0.0/-1.0 V) between the motor A circuit, TCEM harness X1 pin A, and a good ground.
• If the voltage is less than the specified range, test the motor A circuit for an open/high resistance, short to ground or short together condition. If all circuits and connections test normal, test the TCCM.
4. Remove the encoder motor from transfer case. Using a paint pen or marker, place indexing marks on the encoder motor output gear and the mounting surface of the encoder motor.
5. 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.
6. Remove key. Wait 30 seconds. Key ON, engine OFF. Clear codes.
7. Block wheels. Parking brake engaged. Transmission in Neutral. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the encoder motor forward and reverse. When commanded forward, the encoder motor drive gear should rotate in one direction. When commanded reverse, the encoder motor drive gear should rotate in the opposite direction.
• If the encoder motor drive gear is unable to rotate, test the TCEM.
8. Remove the transfer case shift detent plunger plug, spring and plunger. Ensure that the shift detent plunger is not binding or damaged.
9. Verify that the shift shaft is not binding.
10. Inspect the transfer case actuator shaft gear for a binding condition. If binding, remove the transfer case and repair the binding condition.
11. 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. Using a purple probe J 35616-5, attach the red lead from the other EL-49741 - jumper harness to the motor control A terminal of the TCEM, pin A.
3. Using a purple 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 gear in either a clockwise or counter-clockwise rotation depending on battery orientation.
• If the encoder motor drive gear does not rotate, replace the encoder motor.
5. Using the purple probes J 35616-5, test for between 0.3-40 ohms between the motor control A circuit TCEM X1 pin A 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 purple probes J 35616-5, test for greater than 10 ohms between the following circuits and the encoder motor case:
* Motor control A, TCEM harness X1 pin A.
* Motor control B, TCEM harness X1 pin D.
• If outside the specified range, replace the encoder motor.
7. Using the purple probes J 35616-5, test for greater than 1 M ohms between the motor control A circuit, TCEM X1 pin A 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 purple probes J 35616-5, test for greater than 1 M ohms 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 A.
• If outside the specified range, replace the encoder motor.
9. 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 purple probes J 35616-4A, connect a test lamp between the motor control A circuit, TCEM X1 pin A and the ground terminal of EL-49742 - harness, black terminal.
4. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. When commanded forward, the test light should illuminate for 10 seconds and turn OFF. When commanded reverse, 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, reprogram the TCCM. If the DTC continues to set 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, reprogram the TCCM. If the DTC continues to set replace the TCCM.
5. Using the purple 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 Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. 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, reprogram the TCCM. If the DTC continues to set 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, reprogram the TCCM. If the DTC continues to set replace the TCCM.
7. Using the purple probes J 35616-4A, connect a test lamp between the motor control A circuit, TCEM X1 pin A and a good ground.
8. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. When commanded Forward/Counter CW, the test light should illuminate dimly for 10 seconds and turn OFF. When commanded Reverse/Clockwise, the test light should turn OFF.
• If the test light stays ON after the 10 seconds, test the motor control A circuit for a short to voltage. 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 at all, test the motor control A 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.
9. Using the purple probes J 35616-4A, connect a test lamp between the motor control B circuit, TCEM X1 pin D and a good ground.
10. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. When commanded Forward/Counter CW, the test light should turn OFF. When commanded Reverse/Clockwise, the test light should illuminate dimly for 10 seconds and turn OFF.
• If the test light stays ON after the 10 seconds, test the motor control B circuit for a short to voltage. 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 at all, test the motor control B 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.
11. Using the purple probes J 35616-4A, connect a test lamp between the motor control A circuit, TCEM X1 pin A and the B+ terminal of EL-49742 - harness, red terminal.
12. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. When commanded Forward/Counter CW, the test light should illuminate dimly for 10 seconds and turn OFF. When commanded Reverse/Clockwise, the test light should illuminate brightly for 10 seconds and turn OFF.
• If the test light stays ON after the 10 seconds, test the motor control A circuit for a short to voltage. 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 at all, test the motor control A 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.
13. Using the purple 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.
14. Using the Transfer Case Motor Control function of the Special Function feature of the scan tool, command the motor forward and reverse. When commanded Forward/Counter CW, the test light should illuminate brightly for 10 seconds and turn OFF. When commanded Reverse/Clockwise, the test light should illuminate dimly for 10 seconds and turn OFF.
• If the test light stays ON after the 10 seconds, test the motor control B circuit for a short to voltage. 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 at all, test the motor control B 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.
15. 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 Replacement MP 1625/1626-NQF - Transfer Case
* 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
* 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