GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Safari - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 136-NP4 (One Speed Automatic) 🢒 Diagnostic System Check - Transfer Case

These diagnostic procedures will help you to find and repair automatic transfer case (ATC) system malfunctions. This service category also contains information for repairing ATC system malfunctions. For best results, use the diagnostic tables, and follow the sequence listed below:

  1. Perform the Transfer Case Diagnostic System Check. All ATC diagnostics must begin with the Transfer Case Diagnostic System Check. The Transfer Case Diagnostic System Check determines the following:
    2. • Proper SERVICE 4WD indicator operation.
    • Ability of the transfer case shift control module to communicate through the Data Link Connector (DLC)
    • Existence of ATC DTCs
  2. Refer to the diagnostic table as directed by the Transfer Case Diagnostic System Check. The diagnostic tables will help enable you to diagnose any ATC system malfunction. Bypassing these procedures may result in the following:
    3. • Extended Diagnostic Time
    • Incorrect Diagnosis
    • Incorrect Parts Replacement
  3. Repeat the Transfer Case Diagnostic System Check after you perform any repair or diagnostic procedures. This will verify that you correctly performed the repair. This will also ensure that other malfunctions do not exist.

Test Description

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

  1. Lack of communication may be due to a partial malfunction of the Class 2 serial data circuit or due toa total malfunction of the Class 2 serial data circuit. The specified procedure will determine the particular condition.

    2.

  2. A fuse failure will cause no communication this step has you check for this condition.

    3.

  3. This step determines if the fuse blows due to a short to ground on the battery positive voltage circuit.

    4.

  4. This step determines if there is a short to ground in the battery positive circuit causing the fuse to blow.

    5.

  5. This step determines if any DTCs have set.

    6.

  6. This step refers to the table for C0306 for further diagnosis if a transfer case mode changeis causing the fuse to blow.

    7.

  7. The presence of DTCs indicates that the transfer case shift control module has detected a fault. Go to symptomsfor other concerns.

    8.

  8. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specifiedprocedure will compile all the available information before tests are performed.

    9.

  9. Vehicle speed is provided to the transfer case shift control module via Class 2 and can effect thesetting of DTC C0300. Perform the diagnostics for powertrain DTCs P0502 and P0503 first.

    10.

  10. Perform diagnostics for DTC C0300 and C0305 first before addressing other DTCs. DTC C0300 and C0305 can be responsible for setting other DTCs.

Step

Action

Yes

No

1

Install a scan tool.

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up in Data Link Communications

2

  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to establish communication with the transfer case shift control module.

Does the scan tool communicate with the transfer case shift control module?

Go to Step 8

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Check the underhood ATC fuse. Refer to Circuit Protection - Fusible Links in Wiring Systems.

Was the ATC fuse open?

Go to Step 4

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

4

Replace the ATC fuse.

Does the ATC fuse open immediately?

Go to Step 5

Go to Step 7

5

Check the battery positive circuit for a short to ground.

Was the condition found and corrected?

Go to Step 2

Go to Step 6

6

Check for DTCs.

Were any DTCs set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 7

7

  1. Start the Engine
  2. Attempt to shift the transfer case through all modes.
  3. Check the underhood ATC fuse.

Did the ATC fuse open?

Go to DTC C0308

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

8

Select the transfer case shift control module display DTCs function on the scan tool.

Does the scan tool display any DTCs?

Go to Step 9

Go to Symptoms - Transfer Case

9

Does the scan tool display any DTCs which begin with a "U"?

Go to Scan Tool Does Not Communicate with Class 2 Device

Go to Step 10

10

Does the scan tool display DTC P0502 or P0503?

Go to Applicable Powertrain OBD Diagnostic System Check

Go to Step 11

11

Does the scan tool display DTC C0300 or C0305?

Go to DTC C0300 or DTC C0305

Go to Diagnostic Trouble Code (DTC) List