Verify the on-car diagnostics are working by performing the DIAGNOSTIC CIRCUIT CHECK chart in BASIC TESTING article in this section.
Ensure the ECM and SERVICE ENGINE SOON light are functioning properly.
Ensure there are no trouble codes stored, or only intermittent codes are present.
Ensure the fuel control system is operating properly by performing FIELD SERVICE MODE CHECK (except 4.9L) in BASIC TESTING article in this section, or PFI SYSTEM CHECK (4.9L) in the appropriate TESTS W/CODES article in this section.
Perform fuel system pressure test in the BASIC TESTING article in this section.
Perform a careful visual inspection of all systems. After all checks have been performed, verify customer complaint and locate correct symptom. Check items indicated under that symptom. Not all items listed under each symptom apply to all models and systems. These procedures will normally recommend testing of a system or component on vehicle, such as EGR, EST, TCC, etc. See appropriate I - SYS/COMP TESTS article in this section for test procedures.

NOTE: If ECM displays data but engine fails to start, proceed to NO START - ENGINE CRANKS OKAY in BASIC TESTING article in this section.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Preliminary Checks