For 1990-2009 cars

### Test Description

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

1. Lack of communication may be because of 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. The symptom list in Symptoms will determine the correct diagnostic procedure to use.

3. The presence of DTCs which begin with U indicate some other module is not communicating. The specified procedure will collect all the available information before you perform tests.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Perform the Battery Inspection/Test. Refer to Battery Inspection/Test . Does the battery pass the test? | Go to Step 2 | --
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.

Does the scan tool power up?

Go to Step 3

Go to Scan Tool Does Not Power Up in Data Link Communications

3 |

1. Turn ON the ignition, with the engine OFF.
2. Attempt to communicate with each of the following modules on the class 2 serial data circuit:

• | Body Control Module

• | Instrument Panel Module (IPM)

• | Memory Seat Module

• | Onstar (ONS)

• | Radio (IRC)

• | Powertrain Control Module (PCM)

Does the scan tool communicate with all modules on the class 2 serial data circuit?

Go to Step 4

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

4 |

1. Select the Display DTCs function for each module. (If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.)
2. Record all of the displayed DTCs, the DTC status, and the module which set the DTC.

Does the scan tool display any DTCs?

Go to Step 5

Go to Symptoms - Engine Electrical

5 | 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 6
6 | Does the scan tool display DTC B055, B1556, or B1558? | Go to Diagnostic Trouble Code (DTC) List in Body Control System | Go to Diagnostic Trouble Code (DTC) List