DIY: Moderate
Check Engine Light Flashing: What It Means and What to Do
A steady check engine light means a problem was found. A flashing one means a problem is happening right now and is serious enough that the car is asking for attention. Most often it is an engine misfire.
Stay safe first
- Reduce speed and load, avoid hard acceleration and towing, and get to a safe place to stop as soon as you reasonably can.
- If the flashing light comes with an oil pressure warning, a temperature warning, smoke or a burning smell, pull over and shut the engine off.
- Do not keep driving for days with a flashing light. Raw fuel from a misfire can overheat and ruin the catalytic converter.
Flashing light with shaking or a rough, weak engine
Likely causes
- Misfire from worn spark plugs or a failed ignition coil
- Failed fuel injector
- Vacuum leak or low compression on one or more cylinders
What to check
- Read the stored codes. P0300 means random misfire, while P0301 through P0308 point to one cylinder.
- Many parts stores read codes for free.
- If one cylinder is named, swapping that coil with another cylinder's coil is a common way to confirm a bad coil.
Flashing light but the car seems to drive normally
Likely causes
- Intermittent misfire that only shows under certain conditions
- Sensor or fuel delivery problem that comes and goes
What to check
- Treat it as seriously as a rough-running car. A smooth drive does not rule out an active misfire.
- Read the codes and note when the light flashed, such as hard acceleration or going uphill.
Narrow it down for your vehicle
The same symptom can have different likely causes depending on your year, make, model and engine. Describe what you are seeing and CaliperAI will help narrow down the likely causes for your vehicle.
Related guides
General information about this symptom, not a diagnosis of your specific vehicle. Safety-critical work such as brakes, fuel and airbags is best left to a qualified mechanic.