GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Transfer Case Diagnostic System Check

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 indicator (AWD/4WD) lamp operation.
    • Ability of the transfer case shift control module to communicate through the Data Link Connector (DLC)
    • Existence of ATC Diagnostic Trouble Codes (DTC)
  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 no other malfunctions exist.

Circuit Description

The ignition switch supplies Ignition 3 voltage to the transfer case shift control module at connector C1 terminal E10 using the 4WD Fuse. When the ignition switch is first turned to the RUN position, the shift control module responds by performing tests on the ATC system. The shift control module will continue to perform tests on the ATC system during a normal drive cycle. The Service indicator lamp will illuminate if any of the tests fail during the drive cycle and will set a current DTC.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This test checks for proper operation of the serial data line.

    2.

  2. This test will identify the stored diagnostic trouble codes and whether or not they are current or history.

    3.

  3. The SERVICE indicator (AWD/4WD) lamp should turn off after approximately 2 seconds.

Step

Action

Value(s)

Yes

No

1
  1. Turn the ignition to OFF.
  2. Connect a Scan Tool to the Data Link Connector (DLC). Follow the directions in the instruction manual of the scan tool.
  3. Turn the ignition switch to the RUN position.
  4. Attempt to communicate with the transfer case shift control module.

Does the scan tool communicate with the module?

--

Go to Step 2

Go to Data Link Communications System Check

2

Request for ATC diagnostic trouble codes (DTCs) display.

Are there any Current DTCs present in the module?

--

Go to Step 7

Go to Step 3

3

Are there any History DTCs present?

--

Go to Step 11

Go to Step 4

4
  1. Set the parking brake.
  2. Start the vehicle's engine.
  3. Depress the brake pedal and hold.
  4. Place the transmission in Neutral.
  5. Use the scan tool to monitor encoder gear position while depressing each of the transfer case select buttons.

Do all the transfer case select buttons enable the appropriete mode for the encoder gear position?

--

Go to Step 5

Go to Transfer Case Shift Control Switch Inoperative

5

Do any of the Mode Switch Indicator Lamps flash continuously?

Go to Switch Indicator Lamps Flash Continuously

Go to Step 6

6

Do all Mode Switch Indicator Lamps light when their corrisponding switch is depressed?

--

Go to Step 8

Go to Switch Indicator Lamps Do Not Light - One or More

7

Did the Service indicator lamp turn on?

--

Go to Diagnostic Trouble Codes

Go to Service Indicator Inoperative

8

Was the vehicle brought in for a performance concern?

--

Go to Powertrain On Board Diagnostic (OBD) System Check for 4.8L, 5.3L, and 6.0L engines

Go to Step 9

9
  1. Take the vehicle on a road test.
  2. Attempt to duplicate the customer's complaint.
  3. After the road test check for ATC DTCs.

Were there any current ATC DTCs present?

--

Go to Diagnostic Trouble Codes

Go to Step 10

10

Were there any mechanical problems identified on the road test?

--

Go to Transfer Case Mechanical System Diagnosis

System OK

11
  1. A History DTC indicates a malfunction has been repaired (but DTCs were not cleared) or that malfunction is intermittent.
  2. Record any History DTCs set.
  3. Clear ATC DTCs.
  4. Take vehicle on a road test.
  5. Attempt to engage AWD.
  6. After the road test check for ATC DTCs.

Were there any ATC DTCs present?

--

Go to Diagnostic Trouble Codes

Go to Step 12

12

Are the repairs complete?

--

Go to Step 1

--