GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2005 🢒 H2 🢒 Accessories 🢒 Navigation Systems 🢒 DTC B2725

Circuit Description

The mode switch circuit consists of 5 modes. The transfer case shift control module supplies a regulated 5 volts, DC to the switch through the 5-volt regulator circuit. The current travels through the resistor of the currently pressed mode button. The current is then returned to the transfer case shift control module through the switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the mode switch circuit.

When each of the modes are selected they will complete a circuit through their own specific resistor while the button is pressed. The transfer case shift control module continuously monitors the switch input to determine whether the Neutral, Differential Lock, 4HI, 4HI Lock, or 4LO Lock mode was selected by the driver.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2725 ATC Mode Switch Circuit Malfunction

Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is 9-18 volts.

Conditions for Setting the DTC
    • The system constantly monitors the voltage on switch signal circuit.
    • If the system detects a voltage level under 0.3 volt or greater than 0.75 volts, the DTC is logged.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator will remain illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module will clear the current DTC if the condition for setting the DTC is not currently present.
    • A history DTC will clear after 33 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for proper operation of the transfer case mode select switch.

    2.

  2. This step tests the mode switch for proper resistance values in all mode switch states.

    3.

  3. This step tests for proper voltage on the 5-volt reference circuit.

    4.

  4. This step tests the 5-volt reference circuit for an open, high resistance, short to voltage, or short to ground.

    5.

  5. This step tests the switch signal circuit for an open, high resistance, short to voltage, or short to ground.

Step

Action

Values

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Start the engine.
  3. Set the Park brake.
  4. Place the transmission into Neutral.
  5. With a scan tool, observe the Mode Switch Selected parameter.
  6. Select each of the modes.

Does the scan tool indicate that the transfer case is in the mode that is selected?

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Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Disconnect and remove the mode switch.
  2. Connect a DMM between the switch signal and 5-volt reference pins on the switch.
  3. Measure the resistance through the mode switch while pressing and holding each of the mode buttons and comparing values.

Does the DMM indicate all resistance values within the specified ranges?

4 HI 1.8-1.84K ohms

4 HI Lock 707.9-722.2 ohms

4 LO Lock 3.13-3.19K ohms

Differential Lock 64.25-65.6 ohms

Normal 9-9.18K ohms

Go to Step 4

Go to Step 7

4

Check the voltage on the 5-volt reference circuit.

Was the voltage within the specified range?

4.8-5.1 V

Go to Step 6

Go to Step 5

5

Test the 5-volt reference circuit for an open, short to ground, short to voltage, or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 9

Go to Step 8

6

Test the switch signal circuit for a short to voltage, short to ground, open, or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

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Go to Step 9

Go to Step 8

7

Replace the mode switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?

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Go to Step 9

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8

Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup and programming.

Did you complete the repair?

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Go to Step 9

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9
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

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Go to Step 2

System OK