Why is my check engine light flashing?
Short answer
A flashing (blinking) check engine light almost always means the engine is misfiring badly enough to send unburned fuel into the exhaust, which can overheat and destroy the catalytic converter. Ease off the gas, get off the road when it's safe, and don't keep driving it normally until the misfire is diagnosed.
Safety first. If the light is flashing and the car is shaking, losing power, or you smell fuel or something burning, pull over somewhere safe and shut the engine off. Have it towed rather than driven if the flashing doesn't stop. If the temperature or oil pressure warning is also on, stop immediately.
On this page
What a flashing light is telling you
Every car sold in the U.S. since the 1996 model year has an on-board diagnostics system (OBD-II) that watches the engine and emissions equipment. When it finds a fault, it turns on the check engine light. Most of the time the light comes on solid. The system flashes it when it detects a problem that can do damage while you drive, and the most common one by far is a severe engine misfire.
A misfire means one or more cylinders isn’t burning its fuel properly. That unburned fuel goes into the exhaust and reaches the catalytic converter, where it burns. The converter can overheat far past its normal temperature, which can melt its internals and, in the worst case, create a fire risk under the car.
What to do right now
- Back off. Ease off the accelerator and avoid hard acceleration, towing, or climbing steep hills. Misfires are often worst under load.
- Check the other gauges. If the temperature gauge is high, the oil pressure light is on, or the car is shaking hard, pull over and shut it off.
- Get somewhere safe and stop. If the light keeps flashing, the safest call is a tow to a shop rather than driving it there.
- Get the code read. The stored trouble code tells a technician which cylinder or system to look at first.
What it probably isn’t
A loose gas cap is a classic cause of a check engine light, but it turns the light on solid, not flashing. If yours is flashing, don’t assume it’s the gas cap and keep driving.
Flashing vs. solid at a glance
| Light | What it usually means | What to do |
|---|---|---|
| Solid | A fault was found and a code was stored | Get it checked soon; watch for changes in how the car drives |
| Flashing | Active problem that can cause damage, usually a severe misfire | Reduce load, stop when safe, get it diagnosed before driving normally |
Your owner’s manual describes exactly how your car uses the light. If it says something different from this page, go with the manual.
Common follow-up questions
What's the difference between a flashing and a solid check engine light?
A solid light means the car's computer found a fault and stored a code; get it checked soon, but it usually isn't an emergency. A flashing light means a problem is happening right now that can cause damage, most often a severe misfire, so it needs attention immediately.
Can I drive with a flashing check engine light?
Only as far as you need to get somewhere safe, gently and at low load. Continued driving with a severe misfire can overheat the catalytic converter, which is one of the most expensive parts of the exhaust system to replace.
My check engine light flashed and then went solid. Is it fixed?
Not necessarily. Many cars flash the light only while a severe misfire is happening and switch to solid once it eases. The fault is still stored, and the misfire is likely to come back, so get the code read soon.
What usually causes a misfire?
Common causes include worn spark plugs, a failing ignition coil or plug wire, a clogged or leaking fuel injector, a vacuum leak, or low compression. Reading the trouble code (for example P0300 for random misfire, or P0301 to P0308 for a specific cylinder) narrows it down.
How do I find out what code is stored?
Plug an OBD-II scanner into the port under the driver's side of the dashboard. Many auto parts stores will read codes for free, and any repair shop can do it as part of a diagnosis.
Sources
- 1.AAA — The Check Engine Light: Common Causes and How To Fix It
- 2.Consumer Reports — What Does the Check Engine Light Look Like, and What Does It Mean?
- 3.AAA — How to read your dashboard lights
General information only, not a diagnosis. Your owner’s manual comes first. How we write these