Initial Inspection and Diagnostic Overview

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:
- 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:
- 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 flashing the SERVICE indicator (AWD/4WD) lamp for approximately 2 seconds, then turning it OFF, while performing tests on the ATC system. The shift control module will continue to perform tests on the ATC system during a normal drive cycle.


DIAGNOSTIC AIDS
You must diagnose the diagnostic trouble codes in the order specified by the Transfer Case Diagnostic System Check. Failure to do so may result in the following:
- Extended Diagnostic Time
- Incorrect Diagnosis
- Incorrect Parts Replacement


TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
2. This test checks for proper operation of the serial data line.
3. This test will identify the stored diagnostic trouble codes and whether or not they are current or history.
5. The SERVICE indicator (AWD/4WD) lamp should turn off after approximately 2 seconds.