For 1990-2009 cars

Before you begin any diagnostic procedure, always review the system Description and Operation. Reviewing the Description and Operation will help you determine the correct diagnostic procedure when a malfunction exists. Reviewing the Description and Operation will also help you determine if the condition described by the customer is normal operation.

After reviewing the system description and operation, always begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic System Check will provide the following information:

• | The identification of the control modules which command the system

• | The ability of the control modules to communicate through the serial data circuit

• | The identification of any stored diagnostic trouble codes and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.