Diagnostic Procedure

The checks, codes and test charts for each engine are in separate sections of this article. Use the directory at the front of the article to locate the correct page. The headings at the top of the pages will also help you find the tests for your engine. Follow this sequence when testing:

1. Make sure all NON-EEC problems are solved first. Loose wires, low compression, fouled plugs, etc. can cause problems that waste valuable time.
2. Connect test equipment (as described later in this article) to the engine.
3. Perform KEY ON-ENGINE OFF (KOEO) SELF-TEST  for your engine. This checks input and output circuits. If any codes appear, refer to the proper test shown in the reference table for that engine. Start with the first code displayed. If the tests refer you to other checks, perform them as instructed.
4. Perform the Computed Timing Check. This checks the system's spark timing ability.
5. Perform KEY ON-ENGINE RUNNING (KOER) SELF-TEST  . This is a system check with sensors and output devices. If any codes appear, refer to the proper test shown in the reference table.
6. To check for intermittent problems, perform the CONTINUOUS TEST  . This monitors the inputs for shorts and open circuits as you wiggle wires and connectors.