What’s Wrong
with My Car?

Yes — and often you should start that way. A scanner tells you which code was stored, but not necessarily which component failed. Symptoms tell you when the problem occurs, under what conditions, and what changed recently — all of which are more diagnostic than the code alone. Each guide on this page includes first checks you can do with basic hand tools or nothing at all. A scanner becomes most useful after physical checks have narrowed the cause to confirm your diagnosis.

A solid check engine light with no drivability symptoms usually means the PCM detected a fault that exceeds its emissions threshold but isn’t severe enough to affect performance yet — common causes include a loose gas cap (EVAP), a lazy O2 sensor, or a thermostat stuck slightly open. Read the codes with a scanner — many auto parts stores (AutoZone, O’Reilly) will do this for free. If you don’t have a code, use the AI Diagnostic tool above and describe what’s happening.

Three things make a symptom urgent: 1) A flashing check engine light — this means an active misfire is damaging the catalytic converter right now. 2) The temperature gauge is above normal or rising. 3) You smell burning or see white/blue smoke from the exhaust on a warm engine. Everything else can generally wait for a proper diagnosis, though waiting too long often turns a minor repair into a major one. Each guide on this page includes a “Drive or Park” verdict specific to that symptom.

Multiple symptoms together often have a single root cause — this is actually helpful for diagnosis. A lean condition (vacuum leak) causes rough idle, hesitation on acceleration, and poor fuel economy simultaneously. A misfire causes shaking at idle, a flashing CEL, and fuel smell from the exhaust. Start with the most severe symptom — the one that’s most urgent or most noticeable — and the root cause will usually explain the others. Use the AI Diagnostic tool and describe all your symptoms at once for the best result.