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B2725




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
- Active Transfer Case (ATC) Mode Switch Circuit

Diagnostic Fault Information






Circuit/System Description

The automatic transfer case (ATC) multifunction switch consists of 4 modes. The transfer case shift control module (TCCM) supplies a regulated 5 V to the ATC multifunction 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 selected mode indicator control circuit. The TCCM continuously monitors the switch signal low circuit to determine whether a mode change has been requested by the driver.

The T150 transfer case has the following 4 modes:

* 2WD HI
* Neutral
* 4WD HI
* 4WD LO

Conditions for Running the DTC

* Ignition ON.
* System voltage 9-16 V.

Conditions for Setting the DTC

* The TCCM constantly monitors the voltage on switch signal low circuit.
* The voltage detected on the switch signal low circuit is not within a specified range.
* The condition is present for more than 10 seconds.

Action Taken When the DTC Sets

* All transfer case shifting disabled.
* The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
* The transfer case defaults to 4WD HI mode.

Conditions for Clearing the DTC

* The TCCM will clear the current 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 Testing and Inspection.
* EL-49742 - harness is a good source for B+ and ground.

Reference Information
Schematic Reference

Transfer Case Control Schematics
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

Transfer Case 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 Control Module References 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

Key ON, engine OFF. The TCCM runs a 2 second bulb test on all indicators of the ATC multifunction switch at key ON.

Circuit/System Testing

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

1. Key OFF. Disconnect the X1 connector at the ATC multifunction switch. 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 - GM terminal test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.

2. Using the GY probe J 35616-2A, verify that a test lamp illuminates between the ground circuit, ATC multifunction switch X1 pin H and the B+ terminal of EL-49742 - harness , red terminal.

• If the test lamp does not illuminate, test the ground circuit for an open/high resistance. If all circuits and connections test normal, test the TCCM for proper operation.

3. Key ON, engine OFF.
4. Using the GY probe J 35616-2A, verify that a test lamp illuminates between the ignition voltage circuit, ATC multifunction switch X1 pin A and the ground terminal of EL-49742 - harness , black terminal.

• If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If all circuits and connections test normal, test the TCCM for proper operation.

5. Using the GY probe J 35616-2A, test for 4.8-5.2 V between the 5-volt reference circuit ATC multifunction switch X1 pin M, 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.

6. Using the GY probe J 35616-2A, test for 4.8-5.2 V between the 5-volt reference circuit, ATC multifunction switch X1 pin M, and the switch signal low circuit, ATC multifunction switch X1 pin N.

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

7. Using the GY probes J 35616-2A, test for greater than 50 ohm between the 5-volt reference circuit, ATC multifunction switch X1 pin M, and all other pins of the ATC multifunction switch 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.

8. Using the GY probes J 35616-2A, test for greater than 50 ohm between the switch signal low circuit ATC multifunction switch X1 pin 12 and all other pins of the ATC multifunction switch X1, except for the ATC switch signal low circuit ATC multifunction switch X1 pin N.

• 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.

9. Test the ATC multifunction switch for proper operation.

Component Testing

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

ATC Multifunction Switch - 5-Volt Reference and Switch Signal Low
1. Key OFF. Remove the ATC multifunction switch. Refer to: Accessory Switch Replacement Service and Repair.
2. Using the GY probes J-35616-3, measure the resistance for each of the mode positions of the ATC multifunction switch between the 5-volt reference circuit, ATC multifunction switch pin M, and the switch signal low circuit, ATC multifunction switch pin N.

• If the resistance is outside the specified ranges, replace the ATC multifunction switch.

3. Test the TCCM.





ATC Multifunction Switch - Mode LED's
1. Using the GY probes J 35616-3, connect the EL49741 - memory saver harness to the ATC multifunction switch as specified below for the LED being tested. Connecting the harness to the opposite pins will not illuminate the LED.
2. Connect a 9 V battery to the EL49741 - memory saver harness.
3. Verify that only the indicator being tested illuminates.

• If the indicator does not illuminate when tested or the incorrect indicator illuminates, replace the ATC multifunction switch.





TCCM - Mode Switch Circuit
1. Key OFF. Disconnect the X1 connector at the ATC multifunction switch. 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 - GM terminal test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.

2. Key ON, engine OFF.
3. Using the GY probe J 35616-2A, test for 4.8-5.2 V between the 5-volt reference circuit ATC multifunction switch X1 pin M, and the ground circuit, ATC multifunction switch X1 pin H.

• 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, replace the TCCM.
• 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, replace the TCCM.

4. Using the GY probe J 35616-2A, test for 4.8-5.2 V between the 5-volt reference circuit, ATC multifunction switch X1 pin M, and the switch signal low circuit, ATC multifunction switch X1 pin N.

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

5. Using the GY probes J 35616-2A, connect a test light between the ATC multifunction switch harness as specified below for the LED control circuit being tested.
6. Using the Special Function ability of the scan tool, command the affected LED ON and OFF. The test light should turn ON and OFF as commanded.

• If the test light remains illuminated when commanded OFF, test the affected control circuit for a short to ground. If all circuits and connections test normal, replace the TCCM.
• If the test light remains OFF when commanded ON, test the affected control circuit for an open/high resistance or short to voltage. If all circuits and connections test normal, replace the TCCM.





Repair Instructions

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

* Accessory Switch Replacement Service and Repair
* Control Module References Control Module References for transfer case control module replacement, setup, and programming.

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