If your vehicle is showing flashing check engine light, here are the most likely causes and the parts you'll need to fix each one.
Spark plugs ignite the air-fuel mixture in the engine. When they wear out, the gap widens or they become fouled with carbon, causing a severe misfire that triggers a flashing check engine light to warn of catalytic converter damage.
Ignition coils transform battery voltage into the high voltage needed to create a spark. A failing coil will cause a dead cylinder, resulting in a heavy misfire and a flashing check engine light under load.
If spark plugs are dropped (closing the gap), left loose, or if the ignition coil boots are not fully seated and clicked onto the plug during recent maintenance, the engine will immediately misfire.
On older vehicles or specific engine designs, worn spark plug wires can leak high voltage to the engine block instead of delivering it to the spark plug, causing a severe misfire.
If a fuel injector fails electrically or becomes severely clogged, the affected cylinder will not receive enough fuel to combust, causing a lean misfire and a flashing light.
A massive unmetered air leak from a torn hose or blown gasket can lean out the air-fuel mixture so drastically that multiple cylinders begin to misfire simultaneously.
A catastrophic loss of compression due to a burnt engine valve, blown head gasket, or broken piston rings will prevent combustion entirely in that cylinder, causing a permanent, severe misfire.