Check engine light on? What it means and what to do

Solid or flashing: what the difference means

• Solid light: a fault has been detected and stored. Plan to get it checked soon, and watch for any change in how the car drives.
• Flashing light: usually an active misfire. Unburned fuel can overheat and damage the catalytic converter, which is an expensive part. Slow down, avoid hard acceleration and get it checked right away.

Common causes

• A loose, cracked or missing gas cap. Check it first. The light can take a few days of driving to go off after it is tightened.
• Oxygen sensors that have worn out or respond slowly.
• Spark plugs or ignition coils causing misfires.
• Small leaks in the fuel vapor (EVAP) system.
• A dirty or failing mass airflow sensor.
• A catalytic converter that is no longer working efficiently.

Why a code is not a diagnosis

A code reader gives you a code, for example "P0420, catalyst efficiency below threshold". That tells you which system flagged a problem, not which part has failed. The same code can come from a bad sensor, an exhaust leak or the converter itself. Replacing parts based on the code alone often means paying for parts the car didn’t need.

Don’t just clear the code before inspection

Clearing the code turns the light off, but it also resets the car’s readiness monitors. If you go for inspection before they complete, the car can fail as "not ready", and if the fault is still there, the light comes back.

When to pull over

• The light is flashing and the engine is shaking or losing power.
• The temperature gauge is climbing toward hot, or an oil pressure light comes on.
• You smell burning, or see smoke from under the hood.

In any of these cases, pull over somewhere safe, turn the engine off and call for help.

How we handle it here

• We read the codes and the live sensor data, then test the suspected part before recommending anything.
• We explain what we found and give you the price before any work starts. Nothing is done without your approval, and you can ask for a written estimate.
• We are a New York State DMV licensed inspection station, so we can check the readiness monitors before your inspection.
• We are open 24 hours a day, 7 days a week, and we speak English and Spanish.