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MP 1625/1626-NQF - Transfer Case




DTC B2725

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 B2725 08
- Active Transfer Case Mode Switch Circuit - Signal Invalid

Diagnostic Fault Information





Circuit/System Description

The transfer case shift control switch (TCSCS) has 4 modes. The transfer case shift control module (TCCM) supplies a regulated 5 V DC, to the switch through the 5-volt reference circuit. The current travels through the specific resistor of the currently selected mode, each mode has its own resistor. The current is then returned to the TCCM through the switch signal circuit.

The TCCM continuously monitors the switch signal circuit to determine whether a mode change has been requested by the driver.

The NQF transfer case has the following 4 modes:

* 2 Hi
* 4 Hi
* 4 Low
* Neutral

Conditions for Running the DTC

* Ignition ON.
* System voltage 10.5-18 V.

Conditions for Setting the DTC

* The system constantly monitors the voltage on the switch signal circuit.
* If the system detects a voltage level under 0.38 V or greater than 4.86 V for 60 seconds, the DTC is logged.

Action Taken When the DTC Sets

* All shifting is disabled.
* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
* Failure Records will be stored.

Conditions for Clearing the DTC

* The TCCM will clear the current DTC once the condition for setting the DTC is no longer currently 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

Harness EL-49742 is a good source for B+ and ground.

Reference Information
Schematic Reference

Transfer Case Control Schematics (MP 1625/1626-NQF - Transfer Case)
Connector End View Reference

Component Connector End Views (Connector Views)
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 (Programming and Relearning) for scan tool information.
Special Tools

* J 35616 - GM-Approved Terminal Test Kit
* EL-49742 - Battery Voltage (B+) and Ground Source Harness

Circuit/System Verification

1. Key ON, engine OFF.
2. Connect a scan tool.
3. Verify that all mode selections of the Transfer Case Shift Control Switch (TCSCS) match the following parameters in the Data Display feature of the scan tool:

* Mode Switch Selected
* Transfer Case Position
* The corresponding Mode Indicator Light

Circuit/System Testing

1. Key OFF. Disconnect the X1 connector at the Transfer Case Shift Control Switch (TCSCS). Install the EL-49742 Harness.

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.

2. Key ON (Ignition C), engine OFF.
3. Using the L-BU probe J 35616-64B, test for 4.8-5.2 V between the 5-volt reference circuit, TCSCS X1 pin 11, and the ground terminal of EL-49742 Harness, black terminal.

• If the voltage is less than the specified value, test the 5-volt reference circuit for an open/high resistance or short to ground condition. If all circuits and connections test normal, test the TCCM for proper operation.
• If the voltage is greater than the specified value, test the 5-volt reference circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

4. Using the L-BU probe J 35616-64B, test for 4.8-5.2 V between the 5-volt reference circuit, TCSCS X1 pin 11, and the switch signal circuit TCSCS X1 pin 12.

• If the voltage is less than the specified value, test the switch signal 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 switch signal circuit for a short to voltage. If all circuits and connections test normal, test the TCCM for proper operation.

5. Using the L-BU probe J 35616-64B, test for greater than 500 ohm between the 5-volt reference circuit, TCSCS X1 pin 11, and all other pins of the TCSCS X1.

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

6. Using the L-BU probe J 35616-64B, test for greater than 500 ohm between the switch signal circuit TCSCS X1 pin 12, and all other pins of the TCSCS X1.

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

7. Test the TCSCS for proper operation.

Component Testing

1. TCSCS - Mode Switch Circuit
1. Key OFF. Remove the TCSCS.
2. Using the L-BU probe J 35616-65, measure the resistance for each of the mode positions of the TCSCS between the 5-volt reference circuit, TCSCS X1 pin 11, and the switch signal circuit TCSCS X1 pin 12.

• If the resistance is outside the specified ranges, replace the TCSCS.

3. Test the TCCM for proper operation.





2. TCCM - Mode Switch Circuit
1. Key ON, engine OFF. Install the TCSCS.
2. Using the Data Display feature of the scan tool, monitor the Mode Switch Supply and Return Voltages while turning the TCSCS through each mode.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance, short to ground or short together. If all circuits and connections test normal, reprogram the TCCM. If the DTC resets replace the TCCM.
• If the voltage is greater than the specified value, test the affected circuit for a short to voltage. If all circuits and connections test normal, reprogram the TCCM. If the DTC resets replace the TCCM.

3. Perform the circuit/system testing.





Repair Instructions

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

* Transfer Case Shift Control Switch Replacement (Without SLT) (Transfer Case Shift Control Switch Replacement (Without SLT))Transfer Case Shift Control Switch Replacement (With SLT) (Transfer Case Shift Control Switch Replacement (With SLT))
* Control Module References (Programming and Relearning) for TCCM replacement, setup, and programming
* Transfer Case High/Low Clutch Reset (Transfer Case High/Low Clutch Reset) for clutch reset/motor learn procedure after TCCM reprogramming/replacement.

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