Car trouble · Engine & check-engine light

My check engine light is on

A steady check-engine light means the computer stored a trouble code. It is usually not an emergency, but it should be read.

Get to it this week

A starting point, not a diagnosis. Most parts stores read check-engine codes and test batteries for free.

Likely causes — tick the parts you want

A loose or worn gas cap
most likely · Most people can do this
How to check: If the light came on soon after filling up, tighten the gas cap until it clicks. The light can take a few days of driving to go off.
- Check-engine code reading (free service)(Ask the counter to read the check-engine code for free — most parts stores will.)
- Gas cap
A failing oxygen sensor
possible · Doable with tools and a free afternoon
How to check: Have the code read. Oxygen sensor codes are common, and a drop in gas mileage often comes with them.
- Oxygen sensor(Tell the counter the code and which sensor it names, upstream or downstream.)
- Oxygen sensor socket
Worn spark plugs or an ignition coil
possible · Doable with tools and a free afternoon
How to check: A rough idle or a stumble when you accelerate along with the light points toward plugs or coils. The code will name a misfire if so.
- Spark plugs (set)
- Ignition coil
A failing catalytic converter
less likely · A mechanic’s job
How to check: A rotten-egg smell from the exhaust or a code about catalyst efficiency points here. A mechanic should confirm before anything is replaced.

Your car — the counter needs this

YearMakeModelEngine (optional)

VIN (optional, most exact)Which parts store (optional)

If the counter doesn’t have a part, your shopper asks them to order it under your name and messages you the order number. When it comes in, send someone to collect it.

Not quite it?

My check engine light is flashing My oil light is on My engine idles rough or shakes My car hesitates when I accelerate I smell burning oil My car is getting worse gas mileage