For 1990-2009 cars

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

2. The presence of DTC's 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 Interface Unit (VIU).

Does the scan tool communicate with the (VIU)?

Go to Step 3

Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction in Data Link Communications

3 | Select the Vehicle Interface Unit (VIU) 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 Step 5 | Go to Step 6
5 | Does the scan tool display DTC U1500? | Go to Diagnostic Trouble Code (DTC) List/Type | Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction in Data Link Communications
6 | Does the scan tool display DTC B1000, B1004, B1007, or B1009? | Go to Diagnostic Trouble Code (DTC) List/Type 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/Type in Engine Electrical | Go to Diagnostic Trouble Code (DTC) List/Type