GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Envoy - 2WD 🢒 Body 🢒 Stationary Windows 🢒 Diagnostic System Check - Defogger

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. The specified procedure will determine the particular condition.

    2.

  2. The Symptom Table will determine the correct diagnostic procedure to use.

    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.

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 following:
    3. • Body control module (BCM)
    • HVAC control module
    • Liftgate module (LGM) or endgate module (EGM)

Does the scan tool communicate with the modules?

Go to Step 3

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

3

Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.

  1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
  2. Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the Body Control System Description and Operation in Body Control System, for a list of the power mode states that correspond to each ignition switch position.

Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?

Go to Step 4

Go to Power Mode Mismatch in Body Control System

4

Select the display DTCs function on the scan tool for the following modules:

    • HVAC control module
    • LGM or EGM

Does the scan tool display any DTCs?

Go to Step 5

Go to Symptoms - Stationary Windows

5

Does the scan tool display DTCs that begin with "U"?

Go to Diagnostic Trouble Code (DTC) List in Data Link Communications

Go to Step 6

6

Does the scan tool display DTC B1000 or B1440?

Go to Diagnostic Trouble Code (DTC) List in Body Control System

Go to Diagnostic Trouble Code (DTC) List