Diagnostic Circuit Check
The Diagnostic Circuit Check is a starting point in identifying a fuel injection system problem. The ECM will flash Code 12 through the CHECK ENGINE light. This indicates self-diagnostics are working.
Code 12 will not flash 3 times if other codes are stored in memory. Each additional code will flash 3 times. Codes start with the lowest number code. If no codes are present, Code 12 will flash until fuse is removed from fuse block.
Record all codes stored except Code 12. If problem is that engine cranks but will not run, see BASIC TESTING article. If no additional codes were recorded, refer to TESTS W/O CODES article.