Warning lights
Check engine light: what it means when it stays on
A steady check engine light means the engine computer has found a fault that could raise emissions and has stored a code. It is not, by itself, a sign that the car is about to break down.
Can I keep driving with this light on?
Check engine light: on and steady
Moderate: fix within weeks
Keep driving gently and have the code read within days.
- Check that the gas cap is tight and clicked.
- Read the code with a scanner or at a parts store that offers it.
- Look the code up for its severity before deciding how far to drive.
40 CFR 86.1806-05(c): must show "Check Engine", "Service Engine Soon" or an engine symbol; must blink during catalyst-damaging misfire. Your owner's manual prevails for your car.
The check engine light is the malfunction indicator that federal rules require on every car and light truck sold in the US since the 1996 model year. Under 40 CFR 86.1806-05, it must read "Check Engine" or "Service Engine Soon", or show an engine symbol, and it must come on when the on-board diagnostic system detects a fault that could push emissions past the limits or cause a monitored part to fail. A steady light means a fault has been confirmed and a code stored, which any OBD-II scanner reads through the port under the dashboard. A flashing light is different: the same rule makes it blink only during misfire severe enough to damage the catalytic converter, and then you should stop driving. Most steady lights come from emission faults that do not affect safety, such as a fuel vapor leak or an oxygen sensor, but the light also hides any new fault until it is fixed.
After the repair: when does the light go off?
Light off by itself after about
2 days
| Fault-free trips needed | 3 |
| Warm-up cycles before the code can be erased | 40 |
| Stored code gone after about | 40 days |
Federal rule for model years up to 2016 (40 CFR 86.1806-05); a misfire or fuel fault must also stay away under similar conditions. Clearing codes with a scanner also resets the readiness monitors an inspection checks.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
The first five minutes
- Notice whether the light is steady or flashing. Flashing means stop as soon as it is safe; steady means you have time.
- Check the gauges and other lights. Oil pressure, temperature or a red warning are more urgent than the check engine light and change what you should do.
- Check the gas cap if you refueled recently.
- Note how the car drives: shaking, loss of power or strange smells raise the urgency.
The check at the top of this page combines the light, its state and any symptom into a recommendation, from keep driving and book a repair to stop now.
Reading the code
Every car since 1996 has a standard 16-pin diagnostic connector, usually under the dashboard on the driver's side. A scanner reads the stored codes, and the five-character code then tells you the system involved and, for generic codes, a standard meaning. Type it in the code lookup to see its meaning, severity and likely causes. Codes that start with P0, P2 or P3 followed by 4 to 9 are generic; others, such as P1xxx, are defined by each maker.
What the most common codes are
Fuel vapor leaks (P0455, P0442, P0456), the catalytic converter (P0420), oxygen sensors (P0135, P0141), lean running (P0171) and misfires (P0300) account for many lights. Several are cheap to fix, a few are expensive, and the code alone does not tell you which until the cause is found.
Emissions inspections
States that inspect cars with the OBD port fail any car with the light on, and the CARB fact sheet adds that a car fails if its readiness monitors are incomplete, which happens after a code is cleared or the battery disconnected. Fix the fault, then drive normally for about a week before the test.
Warranty
Emission faults on a recent car may be covered at no cost. The federal emission defect warranty runs 2 years and 24,000 miles, and 8 years or 80,000 miles for the catalytic converter and the engine computer (40 CFR 85.2103); California's are longer. The service engine soon page includes a warranty check.