Quick answer
A blinking check engine light combined with shaking almost always means an engine misfire — one or more cylinders are not burning fuel correctly. A flashing light signals that unburned fuel is reaching the catalytic converter, which can overheat and fail quickly, so you should stop driving and address it immediately.
⚠ Important: Stop driving. A flashing check engine light with misfire can melt the catalytic converter within minutes.
Common causes
- Worn or fouled spark plugs failing to ignite the air-fuel mixture
- A failing ignition coil not sending spark to its cylinder
- A vacuum leak leaning out the mixture and causing rough idle
- A clogged or failing fuel injector starving a cylinder of fuel
How to diagnose it
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Read the diagnostic trouble codes
Plug in an OBD2 scanner and read the codes. P0300 (random misfire) or P0301-P0312 (cylinder-specific misfire) confirm the cause.
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Inspect the spark plugs and coils
Remove and inspect the spark plugs for wear, fouling, or a cracked insulator. Swap ignition coils between cylinders to see if the misfire follows the coil.
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Check for vacuum leaks
Listen for hissing around the intake manifold and check rubber hoses for cracks. A smoke test can pinpoint hard-to-find leaks.
When to see a mechanic
- The misfire persists after replacing spark plugs and coils
- You smell raw fuel or sulfur from the exhaust
- The vehicle lacks an OBD2 scanner or you cannot reach the plugs
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