• Flashing Check Engine Light: Likely active misfire. Reduce speed, avoid load, diagnose immediately. Risk of catalytic converter damage.
• Solid Check Engine Light: Usually non‑urgent but should be checked soon. Vehicle may run normally.
• Additional Warning Lights (ABS, SRS, Oil, Temp): Address those systems first as they may be safety‑critical.
1) Check gas cap: Tighten until it clicks. EVAP‑related codes (e.g., P0442, P0455) can set from a loose cap.
2) Listen/feel: Rough idle, hesitation, or smells (fuel/exhaust/rotten egg) help prioritize diagnosis.
3) Basic inspection: Look for loose intake hoses, obvious vacuum leaks, disconnected sensors.
Use a scanner or free parts‑store scan. Record all codes including “pending” and “permanent.” Then look them up above or visit the OBD‑II Codes Index.
• Misfire (P0300–P030X): Check ignition coils, plugs, and vacuum leaks. Avoid heavy throttle. Prolonged misfire can destroy the catalytic converter.
• Catalyst efficiency (P0420/P0430): Rule out exhaust leaks and O2 sensor issues before replacing the converter.
• Lean condition (P0171/P0174): Inspect intake leaks, PCV system, MAF contamination, low fuel pressure.
• EVAP leaks (P0442/P0455): Gas cap, cracked hoses, purge/vent valves; EVAP may not affect drivability but can block inspection.
• Coolant temp (P0128): Stuck‑open thermostat delays warm‑up and keeps monitors “Not Ready.”
Simple faults (gas cap, obvious hose issues, air filter/MAF cleaning) are DIY‑friendly. Complex drivability, electrical diagnostics, or safety systems should be handled by a qualified technician.
• Gas cap: $10–$35
• Spark plugs (set): $40–$120 + labor
• Ignition coil (each): $40–$140 + labor
• O2 sensor: $80–$250 + labor
• Catalytic converter: $500–$1800+ parts + labor
• Thermostat: $30–$120 + labor
• Learn to scan properly: How to Read Codes on Your Car.
• Understand monitors and inspection readiness: Emissions Readiness Monitors Explained.
• Compare scanners: How to Choose an OBD‑II Scanner.
• New to OBD‑II? Start here: OBD‑II Beginner’s Guide.
Is it safe to drive? Usually with a steady light and normal performance, but minimize trips until diagnosed. A flashing light means stop hard driving and diagnose now.
Will the light turn off by itself? If the fault stops occurring, it may clear after several drive cycles—but root cause should still be addressed.
Why did the light return after clearing? The underlying issue persists or is intermittent; the ECU detected it again.
