For 1990-2009 cars

### 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 or a total malfunction of the class 2 serial data circuit. The specified procedure will determine the condition.

2. The presence of DTCs which begin with "U" indicate some other system control module is not communicating.

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 Vehicle Communication Interface Module (VCIM).

Does the scan tool communicate with the VCIM?

Go to Step 3

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

3 | Select the display DTCs function on the scan tool. Does the scan tool display any DTCs? | Go to Step 4 | Go to OnStar Symptom Diagnosis
4 | Does the scan tool display any DTCs which begin with a "U"? | Go to Step 5 | Go to Step 6
5 | Does the scan tool display DTC U1500? | Go to Diagnostic Trouble Code (DTC) List | Go to Diagnostic Trouble Code (DTC) List in Data Link Communications
6 | Does the scan tool display DTC B1000, B1004, B1007, or B1009? | Go to Diagnostic Trouble Code (DTC) List in Body Control System | Go to Step 7
7 | Does the scan tool display DTC B1327 or B1328? | Go to Diagnostic Trouble Code (DTC) List in Engine Electrical | Go to Diagnostic Trouble Code (DTC) List