GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 263-NP1 (Selectable) 🢒 DTC B2725

Circuit Description

The transfer case shift control switch consists of three normally open switches. The transfer case shift control module supplies a regulated 8 volts DC to the switch through the 8 volt reference circuit. The current travels through a 9.09 Kohms resistor located inside the switch. The switch returns current to the transfer case shift control module through the 4WD switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage in order to determine the condition of the shift control switch circuit. If no buttons are pressed, and the transfer case shift control module detects a voltage level outside the possible range, approximately -0.5 to 1.0 volts, for longer than 5 minutes, the transfer case shift control module will set this DTC or if a button is held down or sticks for a period longer than 5 minutes.

When each of the switches is depressed 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, 2HI, and 4LO button selections are made by the driver. Neutral may be obtained if the following conditions are met:

    • The engine is running.
    • The automatic transmission is in neutral or the clutch pedal is depressed on a manual transmission application.
    • The vehicle speed is below (5 km/h) 3 mph.
    • The transfer case is in the 2 HI mode.

Once these conditions have been met, pressing and holding both the 2 HI and 4 LO buttons for 10 seconds will shift the transfer case into neutral, turning on the red neutral indicator lamp.

Conditions for Setting the DTC
    • The system constantly monitors the voltage on the 4WD switch signal circuit.
    • If the system detects a voltage level outside the possible range produced when no buttons are depressed, approximately -0.5 to 1.0 volts, the DTC is logged.

Action Taken When the DTC Sets
    • All shifting will be disabled.
    • The SERVICE 4WD indicator lamp will be commanded 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 no longer exists.
    • 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. This step tests for proper operation of the transfer case shift control switch.

    2.

  2. This step tests for proper voltage supply to the transfer case shift control switch.

    3.

  3. This step tests the transfer case shift control switch for proper resistance values in all switch states.

    4.

  4. This step tests the 4WD switch signal circuit for a short to voltage.

    5.

  5. This step tests the 4WD switch signal circuit for an open or short to ground.

    6.

  6. This step tests the 4WD switch signal circuit for a short to the 8 volt reference circuit.

    7.

  7. Determines whether the 8 volt reference circuit is greater than or less than the specified voltage.

    8.

  8. This step tests the 8 volt reference circuit for a short to voltage.

    9.

  9. This step tests the 8 volt reference circuit for an open or short to ground.

Step

Action

Value(s)

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Was the Diagnostic System Check - Transfer Case performed?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Important: Neutral Range will only be obtained by pressing and holding both the 2 HI and the 4 LO buttons simultaneously for 10 seconds. Refer to Circuit Description.

  1. Install a scan tool.
  2. Start the engine.
  3. Place the transmission into NEUTRAL, or clutch pedal depressed on the manual transmission applications.
  4. Set the park brake.
  5. With a scan tool, observe the Commanded Mode Indicator data parameter in the Transfer Case data list.
  6. Depress each of the shift control switch buttons.

Does the scan tool indicate that the Commanded Mode Indicator data parameter is indicating the correct state?

--

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

Go to Step 3

3

  1. Turn the ignition to OFF.
  2. Disconnect the shift control switch.
  3. Turn the ignition to ON, with the engine OFF.
  4. Measure the voltage from 8 volt reference circuit to a good ground.

Does the voltage measure within the specified value?

7-9 V

Go to Step 4

Go to Step 8

4

  1. Connect a DMM between the 4WD switch signal circuit and the 8 volt reference circuit at the switch.
  2. Measure the resistance through the shift control switch while depressing the range buttons and comparing the values.

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

Normal: 9000-9180 ohms

4 HI: 656-670ohms

2 HI: 1501-1531 ohms

4 LO: 2322-2368 ohms

Neutral: 1015-1035 ohms

Go to Step 5

Go to Step 11

5

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control module.
  3. Turn the ignition ON, with the engine OFF.
  4. Test the 4WD switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 6

6

Test the 4WD switch signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 7

7

Test the 4WD switch signal circuit for a short to the 8 volt reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

8

Was the voltage measured in Step 3 greater than the specified value?

9 V

Go to Step 9

Go to Step 10

9

  1. Turn OFF the ignition.
  2. Disconnect the transfer case shift control module.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the 8 volt reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10

  1. Turn OFF the ignition.
  2. Disconnect the transfer case shift control module.
  3. Turn ON the ignition, with the engine OFF.
  4. Test the 8 volt reference circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the transfer case shift control switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

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

Did you complete the replacement?

--

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Setting the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK