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C0327

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DTC C0327

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 C0327
- Encoder Circuit

Diagnostic Fault Information





Circuit/System Description

The transfer case encoder motor (TCEM) consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the rear of the transfer case. When activated, the TCEM rotates the control actuator shaft in the transfer case either clockwise or counterclockwise. This rotation of the control actuator shaft causes the shift forks and collar assemblies to move, allowing a range/mode change. The encoder motor is controlled through a 12 V circuit provided by the transfer case shift control module (TCCM). This circuit consists of a driver on both the motor control A and motor control B circuits. The encoder motor is bi-directional to allow the motor to shift the transfer case between 2WD HI, 4WD HI, 4WD LO and Neutral positions.

The encoder is part of the TCEM assembly and is replaced only as an assembly. The transfer case control actuator shaft represents the mode/range position that the transfer case is currently in.

TCCM has four encoder channels, A, B, C, and P. The TCCM supplies 12 V to each of the four encoder signal circuits. When a mode/range change is made, a combination of these encoder channels are pulled to ground. This allows the encoder to convert the physical position of the control actuator shaft into electrical signals. The TCCM interprets the state of the encoder signal circuits (HI/Low) to determine what position the transfer case is in. These combinations of circuits translate into 2WD HI, 4WD HI, 4WD LO, Neutral, or whether the motor is still in transition between gears.

This sensor is made up of the following 5 circuits:

* Channel A Encoder - Signal
* Channel B Encoder - Signal
* Channel C Encoder - Signal
* Channel P Encoder - Signal
* Ground

Conditions for Running the DTC

* Ignition ON.
* System voltage 10-16 V.

Conditions for Setting the DTC

* The TCCM detects an invalid combination of encoder signal feedbacks when compared to a predefined mode/range strategy in the read only memory (ROM) within the TCCM.
* The fault must remain current for 30 seconds.

Action Taken When the DTC Sets

* All motor activity will stop.
* All accessory switch mode indicators will be commanded OFF.
* The SERVICE 4WD indicator will be ON until the fault is corrected.
* If a new mode is requested by the driver with either a current or history DTC, the transfer case shift control module (TCCM) will only allow a shift to 2WD HI mode. After which the TCCM will not allow any further mode changes.

Conditions for Clearing the DTC

* The TCCM will clear the DTC once the conditions for setting the DTC no longer exist.
* 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

* A low battery condition or charging system that is faulty could set this DTC. Refer to Battery Inspection/Test (Battery Inspection/Test) and Charging System Test (Charging System Test).
* Harness EL-49741 is a good source for 9 V.
* Harness EL-49742 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 Views)
Description and Operation

Transfer Case Description and Operation (Description and Operation)
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)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

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

* J 35616 - GM-Approved Terminal Test Kit
* EL-49741 - 9 V+ Power Source Harness
* EL-49742 - Battery Voltage B+ and Ground Source Harness

Circuit/System Verification

1. Key ON, engine OFF. The TCCM runs a 2 second bulb test on all indicators of the TCSCS at key ON.
2. Apply parking brake. Transmission in Neutral. (Manual transmissions also require that the clutch be depressed.)
3. One at a time, command each mode/range using the automatic transfer case (ATC) multifunction switch. You should be able to hear the encoder motor as it changes mode/range. The selected mode/range indicator should laminate. The 4WD LO and Neutral indicator may flash for an extended period of time with engine OFF.
4. Engine ON. Transmission in Neutral. (Manual transmissions also require that the clutch be depressed.)
5. One at a time, command each mode/range using the automatic transfer case (ATC) multifunction switch. You should be able to hear the encoder motor as it changes mode/range. The selected mode/range indicator should laminate. The ATC should shift into and out of each mode/range.

Circuit/System Testing

Note: You must perform the Circuit/System Verification before proceeding to Circuit/System Testing.

1. Verify that the TCCM fuse, and the Cruse fuse, underhood fuse block, are not open.

• If the TCCM fuse is open, test the battery positive voltage, TCCM harness X1 pin 8, for a short to ground.
• If the Cruse fuse is open, test the ignition voltage circuit, TCCM harness X2 pin 10, for a short to ground.

2. Key OFF. Disconnect the X1 connector at the transfer case encoder motor (TCEM).
3. Install a scan tool.
4. Install the EL-49742 harness.
5. Key ON, engine OFF.

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.

6. Using the GY probe J 35616-2A, test for a true B+ (+0.0/-1.0 V) between the motor control A circuit, TCEM X1 pin C and the B+ terminal of the EL-49742 harness, red terminal.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM for proper operation.

7. Using the GY probe J 35616-2A, test for a true B+ (+0.0/-1.0 V) between the motor control B circuit, TCEM X1 pin B and the B+ terminal of the EL-49742 harness, red terminal.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM for proper operation.

8. Using the GY probe J 35616-2A, test for a true B+ (+0.0/-1.0 V) between the TCCM Ground circuit, TCEM X1 pin E and the B+ terminal of the EL-49742 harness, red terminal.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the TCCM for proper operation.

9. Using the GY probes J 35616-2A, test for a diagnostic B+ (+0.0/-1.0 V) between the channel A encoder - signal circuit, TCEM X1 pin A and the TCCM ground circuit, TCEM X1 pin E.

• If the voltage is less than the specified value, test the encoder low reference circuit for an open/high resistance, short to ground or short together. If all circuits and connections test normal, test the TCCM for proper operation.
• If the voltage is greater than the specified value, test the encoder low reference circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

10. Using the GY probes J 35616-2A, test for a diagnostic B+ (+0.0/-1.0 V) between the channel B encoder - signal circuit, TCEM X1 pin F and the TCCM ground circuit, TCEM X1 pin E.

• If the voltage is less than the specified value, test the encoder low reference circuit for an open/high resistance, short to ground or short together. If all circuits and connections test normal, test the TCCM for proper operation.
• If the voltage is greater than the specified value, test the encoder low reference circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

11. Using the GY probes J 35616-2A, test for a diagnostic B+ (+0.0/-1.0 V) between the channel C encoder - signal circuit, TCEM X1 pin G and the TCCM ground circuit, TCEM X1 pin E.

• If the voltage is less than the specified value, test the encoder low reference circuit for an open/high resistance, short to ground or short together. If all circuits and connections test normal, test the TCCM for proper operation.
• If the voltage is greater than the specified value, test the encoder low reference circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

12. Using the GY probes J 35616-2A, test for a diagnostic B+ (+0.0/-1.0 V) between the channel P encoder - signal circuit, TCEM X1 pin H and the TCCM ground circuit, TCEM X1 pin E.

• If the voltage is less than the specified value, test the encoder low reference circuit for an open/high resistance, short to ground or short together. If all circuits and connections test normal, test the TCCM for proper operation.
• If the voltage is greater than the specified value, test the encoder low reference circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

13. Key OFF.
14. Using the GY probes J 35616-2A, test for >100 ohm between the channel A encoder - signal circuit, TCEM X1 pin A and all other pins of the TCEM X1 connector.

• If the resistance is less than the specified value, test the affected circuits for a short together condition. If all circuits and connections test normal, test the TCCM for proper operation.

15. Using the GY probes J 35616-2A, test for >100 ohm between the channel B encoder - signal circuit, TCEM X1 pin F and all other pins of the TCEM X1 connector.

• If the resistance is less than the specified value, test the affected circuits for a short together condition. If all circuits and connections test normal, test the TCCM for proper operation.

16. Using the GY probes J 35616-2A, test for >100 ohm between the channel C encoder - signal circuit, TCEM X1 pin G and all other pins of the TCEM X1 connector.

• If the resistance is less than the specified value, test the affected circuits for a short together condition. If all circuits and connections test normal, test the TCCM for proper operation.

17. Using the GY probes J 35616-2A, test for >100 ohm between the channel P encoder - signal circuit, TCEM X1 pin H and all other pins of the TCEM X1 connector.

• If the resistance is less than the specified value, test the affected circuits for a short together condition. If all circuits and connections test normal, test the TCCM for proper operation.

18. Using the GY probes J 35616-2A, test for >100 ohm between the ground circuit, TCEM X1 pin E and all other pins of the TCEM X1 connector.

• If the resistance is less than the specified value, test the affected circuits for a short together condition. If all circuits and connections test normal, test the TCCM for proper operation.

19. Remove the encoder motor from the transfer case. Using a paint pen or marker, place indexing marks on the control actuator lever shaft receiver and the mounting surface of the encoder motor.
20. Inspect the control actuator lever shaft receiver for a binding condition. If binding, remove the transfer case and repair the binding condition. A flat blade screwdriver, inserted into the receiver, should turn a little bit clockwise and counter clockwise.
21. If all circuits and connections test normal, test the TCCM.

Component Testing

Encoder Motor - Motor A and Motor B
1. Remove the encoder motor from the transfer case. Using a paint pen or marker, place indexing marks on the control actuator lever shaft and the mounting surface of the encoder motor.
2. Using a GY probe J 35616-3, attach the red lead from the EL-49741 harness to the motor control B terminal of the transfer case encoder motor, pin B.
3. Using a GY probe J 35616-3, attach the black lead from this same harness to the motor control A terminal of the transfer case encoder motor, pin C.
4. Touch the battery terminals of a 9-volt battery to the battery terminals of the jumper harness. This will rotate the encoder motor shaft in either a clockwise or counter-clockwise rotation depending on battery orientation.

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

Encoder Motor - Encoder Circuits
1. Remove the encoder motor from the transfer case. Using a paint pen or marker, place indexing marks on the control actuator lever shaft and the mounting surface of the encoder motor.
2. Using a GY probe J 35616-3, attach the black lead from this same harness to the motor control A terminal of the transfer case encoder motor, pin C.
3. Prepare to touch the battery terminals of the 9-volt battery to the battery terminals of the jumper harness. This will rotate the encoder motor shaft in either a clockwise or counter-clockwise rotation depending on battery orientation.
4. While rotating the encoder motor, measure the resistance between the following pin combinations. The resistance should measure either [5.0 ohm or]1 M ohm. (A momentary measurement of up to 40 ohm may occur while rotating the motor, but resolve itself when stationary on some multimeters.)

• If the resistance does not measure as stated, replace the TCEM.

TCEM
* Pin A to pin E
* Pin A to pin F
* Pin A to pin G
* Pin A to pin H
* Pin E to pin F
* Pin E to pin G
* Pin E to pin H
* Pin F to pin G
* Pin F to pin H
* Pin G to pin H

5. Test the TCCM.

TCCM
1. Remove the TCEM from the transfer case. Using a paint pen or marker, place indexing marks on the control actuator lever shaft and the mounting surface of the encoder motor.
2. Connect the TCEM to the TCEM harness. Position the TCEM so it can be seen from the side on the vehicle.
3. Key ON, engine OFF. (Manual transmission requires clutch to be depressed also.)
4. Monitor the TCEM shaft while using the multifunction switch to shift into each mode. The TCEM shaft should rotate with each selection.

• If the encoder motor does not rotate, replace the TCEM.

Repair Instructions

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

* Transfer Case Encoder Motor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for transfer case shift control module replacement, setup, and programming.

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