For 1990-2009 cars

Important: The following steps must be completed before using the symptom tables:

1. Perform the Diagnostic System Check for the subsystem exhibiting symptoms. The subsystem Diagnostic System Check will identify where to begin diagnosis of the data link communications system.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to Data Link Communications Description and Operation .

### Visual/Physical Inspection

• | Inspect for aftermarket devices that could affect the operation of the serial data communications system. Refer to Checking Aftermarket Accessories .

• | Inspect the easily accessible systems or visible system components for obvious damage or conditions that could cause the symptom.

### Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

### Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:

Scan Tool Does Not Power Up