GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 236-NP8 🢒 Transfer Case Shift Control Switch Inoperative

Circuit Description

The range/mode switch circuit consists of 4 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 K ohms resistor located inside the switch, then returns current to the transfer case shift control module through the switch signal circuit.

When each of the switches is depressed, they 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, 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.
    • The vehicle speed is below 5 km/h (3 mph).
    • The transfer case is in the 2HI mode.

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

Test Description

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

  1. This step tests the functionality of the mode/range buttons.

    2.

  2. This step tests the ability of the modules to operate the transfer case modes.

Step

Action

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?

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. 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.

  3. Place the transmission into Neutral.
  4. Set the parking brake.
  5. Observe the mode switch selected states on the scan tool while depressing and holding each of the mode buttons.

Does the state change with the press of any of the mode buttons?

Go to Step 4

Go to Step 3

3

  1. Use a scan tool in order to command through the ranges of the mode switch.
  2. With a scan tool, command through all mode switch selected indicator states.

Does the Mode Indicator state change?

Go to Step 4

Go to Step 5

4

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

Did you complete the replacement?

Go to Step 6

--

5

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 replacement?

Go to Step 6

--

6
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle in order to determine if the symptom has been corrected.

Is the symptom still present?

Go to Step 2

System OK