A check engine light can come on for a wide range of reasons, from something simple and inexpensive to fix to more serious engine or emissions problems. Here are common causes and what to do next. What it might mean

• Loose or missing gas cap: This is a frequent, inexpensive culprit that can trigger the light.
• Oxygen sensor or other emissions system issues: Sensor failures or exhaust problems are common triggers.
• Faulty spark plugs, ignition coils, or wires: Misfires can illuminate the light.
• Catalytic converter problems: Issues here can trigger the light and affect emissions and performance.
• Mass airflow sensor or other engine sensors: Sensor faults can cause the engine computer to flag a fault.
• Fuel system problems: Contaminated fuel or a failing fuel injector can set off the light.
• Cooling or engine problems: Severe overheating or internal engine faults can also trigger warning codes.

What to do now

• If the light is solid (not flashing): You can usually continue driving, but schedule a diagnostic check soon to read the onboard fault codes (OBD-II) and identify the specific issue.
• If the light is flashing: This indicates a misfire severe enough to warrant immediate attention. Reduce speed and drive cautiously to a repair shop or service center as soon as possible to avoid damaging the catalytic converter or engine.
• Check basic items first: Ensure the gas cap is properly tightened and not damaged. If the cap was loose, tightening it may extinguish the light after a few driving cycles.
• Get a diagnostic code: A mechanic or auto parts store can read the error codes from the vehicle’s computer. The codes point to the system or component involved (for example, P0300 series codes for misfires, P0420 for catalytic converter inefficiency, etc.).
• Plan a fix based on the code: Depending on the code, the fix could be as simple as replacing a faulty spark plug or sensor, or more involved like addressing an exhaust leak or catalytic converter issue.

Safety and cost notes

• Ignoring the light can lead to worse fuel economy, potential damage, and failed emissions tests.
• Some causes are inexpensive (gas cap, sensor) while others can be more costly (catalytic converter, ignition components). A precise diagnosis is essential.

If you’d like, share your vehicle’s year, make, model, and whether the light is steady or flashing, plus any symptoms (rough running, rough idle, reduced power, noise, strange smells). I can help interpret typical fault codes and suggest a targeted next step.