Engine
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    car
    truck

    Why Is My Check Engine Light Flashing?

    Typical repair cost: $80–$2,000

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    Common Symptoms

    Flashing CEL
    Engine shaking
    Loss of power
    Unusual exhaust smell
    Codes P0300-P0308

    Most Likely Causes

    1

    Active misfire

    Flashing CEL means raw fuel is dumping into the catalytic converter — pull over.

    2

    Failed ignition coil

    Single-cylinder misfire that can be diagnosed by swapping coils between cylinders.

    3

    Bad spark plug

    Fouled or worn plug causes misfire under load.

    4

    Vacuum or intake leak

    Lean misfire across multiple cylinders.

    5

    Failed injector

    No fuel to a cylinder triggers a hard misfire.

    How a Shop Diagnoses It

    1. 1.Pull codes immediately — P030x identifies misfiring cylinder.
    2. 2.Swap coil/plug to isolate ignition vs fuel.
    3. 3.Check fuel trims and intake for vacuum leaks.

    When to see a professional

    A flashing CEL is the highest-urgency engine warning. Stop driving — continued operation destroys the catalytic converter.

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    Parts pros use for this job

    Scan your own codes

    A basic OBD-II scanner pays for itself the first time you avoid a diagnostic fee.

    • Bluetooth scanners for any phone
    • Live data & freeze frame
    • Reset check engine light

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