Why is my check engine light on?

The check engine light (CEL) is your car’s way of saying “something’s wrong”—but it can mean anything from minor to serious. Here's a breakdown of the most common reasons it turns on:

1. Loose or Faulty Gas Cap

  • One of the most common and simple causes.

  • A loose gas cap can disrupt fuel system pressure.

  • Fix: Tighten the cap or replace it if damaged.

2. Oxygen Sensor Failure

  • The O2 sensor monitors fuel mixture and emissions.

  • If it fails, your car may burn more fuel or fail an emissions test.

  • Fix: Replace the sensor (often under $200).

3. Catalytic Converter Issues

  • This component reduces exhaust emissions.

  • A failing converter can cause poor performance or strong exhaust smells.

  • Fix: Expensive—may cost $1,000+ to replace.

4. Faulty Spark Plugs or Ignition Coils

  • Spark plugs ignite fuel in the engine.

  • Bad plugs/coils can cause rough idling, misfiring, or poor gas mileage.

  • Fix: Replace spark plugs/coils (relatively affordable maintenance).

5. Mass Airflow Sensor (MAF) Failure

  • This sensor manages how much air enters the engine.

  • If faulty, your car might hesitate or stall.

  • Fix: Replace the MAF sensor.

6. Vacuum Leaks

  • Hoses in your engine can crack or come loose.

  • A vacuum leak can throw off fuel-air balance.

  • Fix: Requires inspection and sometimes replacing hoses or intake gaskets.

7. Transmission or Engine Trouble

  • A CEL might also indicate deeper engine or transmission issues.

  • Fix: Immediate diagnostic scan recommended.

What You Should Do:

  1. Check the gas cap first – tighten or replace.

  2. Get a diagnostic scan – Come to lifetime Automotive and we can diagnose the problem.

  3. Don’t ignore it – especially if the light is flashing (indicates active engine misfire or major issue).

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