Basic Diagnostic Procedure

The diagnostic charts at the end of article provide a logical sequence for determining system failures. Any diagnosis of the DEC system should be performed in the following order:

1. Ensure that all engine systems not related to the DEC system are operating properly. This should include a careful visual underhood inspection including: all vacuum hoses for correct routing, pinches, cuts, or disconnects; all wires in engine compartment for correct and good connections, burned or chaffed spots, pinched wires, or contact with sharp edges or hot exhaust manifolds.
2. Start with "DIAGNOSTIC CIRCUIT CHECK" chart and continue diagnosis as indicated in chart. This check will either verify proper DEC system and ECM operation, or direct you to a specific trouble code chart(s) or another DEC system chart.