Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Pretest Inspection - PFI: Notes
If PFI system components fail, interruption of fuel supply will result. Engine may be hard to start or not start at all. Unstable idle and/or poor driveability will be noticed. If any of these conditions are present, first perform basic engine checks (ignition, engine adjustments, etc.). See BASIC TESTING article.
If no faults were found while performing basic diagnostic procedures, go to ENTERING SELF-DIAGNOSTICS in this article. If no fault codes or only pass codes are present, go to TESTS W/O CODES (TROUBLE SHOOTING) article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).
The self-diagnostic system monitors all input signals from each sensor. If an abnormal input signal occurs, that item is memorized by the ECU and given a code number. See DIAGNOSTIC FAULT CHARTS in this article. Fault codes can be confirmed by using a voltmeter.
If 2 or more systems are non-functional, they are indicated by order of increasing code number. Indication is made by 12-volt pulses of voltmeter pointer. A constant repetition of short 12-volt pulses indicates system is normal. If system is abnormal, voltmeter will pulse between zero and 12 volts.
System malfunctions encountered are identified as either hard failures or intermittent failures as determined by the ECU.
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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.