Diagnostic Circuit Check

This check ensures that the self-diagnostic system is working, determines that the trouble codes will display and guides diagnosis to other problem areas. Use this test if complaint is "CHECK ENGINE" light related, while noting the following:

• If code "51" is displayed, refer to PROM removal and installation in this article for diagnosis of code.
• If codes "51", "54" or "55" are displayed in addition to other code(s), refer to diagnostic chart for "50" series code first, then go to lowest numbered code.