GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Colorado Pickup - 2WD 🢒 Driveline/Axle 🢒 Front Drive Axle 🢒 Diagnostic System Check - Transfer Case

These diagnostic procedures help you 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 Diagnostic System Check - Transfer Case. All transfer case diagnostics must begin with the Diagnostic System Check - Transfer Case. The Diagnostic System Check - Transfer Case determines the following:
    2. • Proper SERVICE 4WD indicator operation.
    • The ability of the transfer case shift control module to communicate through the Data Link Connector (DLC).
    • The existence of transfer case DTCs.
  2. Refer to the diagnostic table as directed by the Diagnostic System Check - Transfer Case. The diagnostic tables 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 Diagnostic System Check - Transfer Case after you perform any repair or diagnostic procedure. This verifies that you correctly performed the repair. This also ensures that other malfunctions do not exist.

Test Description

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

  1. This step inspects for lack of communication that may be due to a partial malfunction of the Class 2 serial data circuit or due to a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.

    2.

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

    3.

  3. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure compiles all the available information before tests are performed.

    4.

  4. Vehicle speed is provided to the transfer case shift control module via Class 2 and can effect transfer case shifting. Perform the diagnostics for powertrain DTC P0502 and DTC P0503 first.

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 3

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

3

Select the Transfer Case Shift Control Module display DTCs function on the scan tool.

Does the scan tool display any DTCs?

Go to Step 4

Go to Symptoms - Transfer Case

4

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

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

Go to Step 5

5

Does the scan tool display DTC P0502 or P0503?

Go to Applicable Powertrain OBD Diagnostic System Check

Go to Symptoms - Transfer Case