GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Astro - 4WD 🢒 Body and Accessories 🢒 Body Control System 🢒 Diagnostic System Check

Test Description

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

  1. Lack of communication 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 will determine the particular condition.

    2.

  2. Tests for the presents of DTCs. The presence of DTCs indicates that the transfer case shift control module has determined that a fault has taken place within it's system.

    3.

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

    4.

  4. The presence of DTCs which are related to the powertrain's vehicle speed sensor has the potential of setting transfer case codes due to information that is shared by the transfer case shift control module via Class 2. These codes should be repair first.

    5.

  5. The presence of DTC C0300 or C0305 should be repaired before addressing other transfer case 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

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

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

4

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 5

5

Does the scan tool display DTC P0502 or P0503?

Go to OBD Diagnostic System Check

Go to Step 6

6

Does the scan tool display DTC C0300 or C0305?

Go to DTC C0300 Rear Speed Sensor Malfunction or DTC C0305 Front Speed Sensor Malfunction

Go to Diagnostic Trouble Codes