GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 226-NP8 🢒 DTC B2725

Circuit Description

The range/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 travel through the resistor of the currently active mode. 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. The transfer case shift control module continuously monitors the switch input to determine whether the 4HI, AUTO 4WD, 2HI, or 4LO mode was selected by the driver.

Conditions for Setting the DTC
    • The system constantly monitors the voltage on switch signal circuit.
    • If the system detects a voltage level under 0.1 volt or greater than 4.9 volts, the DTC is logged.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator will be latched on 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 100 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. Tests for proper operation of the transfer case mode select switch.

    2.

  2. Tests the mode switch for proper resistance values in all mode switch states.

    3.

  3. Tests the switch signal wire for a short to ground, short to voltage, or high resistance

Step

Action

Values

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Did you perform the Diagnostic System Check-Transfer Case?

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Go to Step 2

Go to Diagnostic System Check - Transfer Case

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 4WD indicator modes in the tech 2 transfer case data list.
  6. Select each of the modes.

Does the scan tool indicate that the 4WD indicators are in the correct state?

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

Go to Step 3

3

  1. Connect a DMM between the selector mode switch signal and voltage from the 5-volt regulator circuit at the switch.
  2. Measure the resistance through the selector mode switch while selecting the modes and comparing values.

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

2 HI: 230-245 ohms

AWD: 526-580 ohms

4 HI: 1,042-1,107 ohms

4 LO: 2,039-2,165 ohms

Neutral: 4,467-4,743 ohms

Go to Step 4

Go to Step 5

4

Test the switch signal for a short to voltage, short to ground, 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 7

Go to Step 6

5

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

Is the repair complete?

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Go to Step 7

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6

Important : After transfer case shift control module replacement and reprogramming make sure all doors are closed and the key is out of the ignition, then open and close the doors again and wait 2 minutes to avoid setting false DTCs.

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement and Transfer Case Shift Control Module Reprogramming .

Is the repair complete?

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Go to Step 7

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7

  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