Automotive Part PickerCar Problems › Check Engine Light is illuminated or flashing

Check Engine Light is illuminated or flashing: Causes & How to Fix It

If your vehicle is showing check engine light is illuminated or flashing, here are the most likely causes and the parts you'll need to fix each one.

Most likely causes

Loose or Missing Gas Capminor

A loose, damaged, or missing gas cap allows fuel vapors to escape, triggering a minor EVAP system leak code. This is the most common and easiest to fix cause of a solid check engine light, often occurring right after refueling.

Worn Spark Plugs or Ignition Coilsurgent

Worn spark plugs or failing ignition coils cause the engine to misfire. If the check engine light is actively flashing, this is almost always the cause and requires immediate attention to prevent severe catalytic converter damage.

Faulty Oxygen (O2) Sensoraddress soon

Oxygen sensors measure the amount of unburned oxygen in the exhaust to adjust the fuel mixture. They naturally degrade over time, leading to decreased fuel economy and an illuminated check engine light.

Mass Air Flow (MAF) Sensor Issueaddress soon

The MAF sensor measures air entering the engine. It can fail from dirt buildup or be triggered if the sensor was accidentally left unplugged after checking or replacing the engine air filter.

EVAP Purge or Vent Valve Failureminor

These valves control the flow of fuel vapors from the gas tank into the engine to be burned. When they stick open or closed due to wear, they trigger an emissions code.

Variable Valve Timing (VVT) Solenoid Failureaddress soon

VVT solenoids adjust engine timing based on oil pressure. Low oil levels, dirty oil from missed oil changes, or a failed solenoid can trigger the light and cause sluggish performance.

Catalytic Converter Failureaddress soon

The catalytic converter reduces exhaust emissions. If it fails, it is usually a secondary failure caused by ignoring other issues like engine misfires or burning oil for too long.

Related problems

Not sure which it is? Run the full AI diagnosis →