Why is my check engine light on?
A check engine light means the vehicle's computer stored a trouble code because a sensor reading fell outside the expected range. A steady light means get it checked soon. A flashing light means stop driving and call us.
The Detail
What's Actually Going On
The light itself does not tell you what is wrong. It tells you the computer noticed something and saved a code about it. Pulling that code is the starting point, not the diagnosis. A code points to a circuit or a system, and the actual failure can be the part, the wiring, a connector, a vacuum leak, or a second problem making the first one look worse than it is.
That is the difference between reading a code and diagnosing a vehicle. A parts-store scan will tell you a code is stored. It will not tell you whether the oxygen sensor is bad or whether the oxygen sensor is reporting accurately on an engine that is running lean for another reason. Replacing parts based on a code alone is how people spend money twice.
A steady light is not an emergency, but it is not something to ignore for six months either. A flashing light usually means a misfire severe enough to damage the catalytic converter, and that turns a modest repair into an expensive one quickly. If your light is flashing, get off the road and call us.
Checklist
Common reasons the light comes on
- A loose, cracked, or worn gas cap
- A failing oxygen sensor
- A misfire from spark plugs, coils, or wires
- A failing mass airflow sensor
- A vacuum or intake leak
- A catalytic converter that has degraded
- An EVAP system leak
- A weak battery or charging problem confusing the sensors
Next Step
What We'd Do
Bring it in and we will pull the codes, test the circuits, and tell you what is actually wrong before anyone touches a part. You get the diagnosis and the price first.
More Answers
Other Questions We Get
Let's Take a Look
Bring it by and we'll tell you what's actually wrong, what it costs, and what can wait.