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P0301Cylinder 1 misfire detected

Content reviewed: Content reviewed by a heavy-duty technician. About our editorial approach

OK to drive

— A single-cylinder miss on cylinder 1 is often driveable at light load, but a flashing MIL means unburned fuel can damage the catalyst—ease off until the miss is fixed.

What does this severity mean?

General guidance only — not a substitute for a professional inspection or official roadside / out-of-service criteria (e.g. CVSA OOSC) in your jurisdiction.

Part of system: Electrical sensing & powertrain inputs · Wire gauge & ampacity tool

Usually changes how the vehicle drives, shifts, or feels rather than creating an immediate emergency. P0301 flags a combustion miss specifically on cylinder 1, not a random multi-cylinder event. The ECM counts crankshaft acceleration glitches tied to that firing order position, so drivers feel a rhythmic shake at idle and a flat spot under light throttle while fuel trims on the affected bank drift. Start by swapping the cylinder-1 coil and plug with another cylinder to see if the miss follows the parts, then leak-down or relative compression on cylinder 1, and only then chase injector balance or wiring at the coil connector. Oil-flooded plugs after short cold trips and cracked coil boots are frequent winter culprits on coil-on-plug engines. Sort among failed coil-on-plug or cracked boot on cylinder 1, worn, fouled, or wrong-gap spark plug in cylinder 1, and low compression from burned valve or ring wear on cylinder 1 with a methodical road-test mindset. Begin with swap cylinder-1 coil and plug with another cylinder and retest, continue with run relative compression or leak-down focused on cylinder 1, and consider cylinder-1 ignition coil and dielectric grease only after the data still condemns that part.

Parts that may be involved

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Vehicles often affected

Frequent on coil-on-plug engines after oil seepage into plug wells, and on vehicles that idle a lot in cold weather with aged plugs on cylinder 1.

Typical symptoms

  • Rhythmic idle shake timed to cylinder-1 firing
  • Misfire counters climb only on cylinder 1 in Mode $06 or OEM PID
  • Fuel smell or raw hydrocarbon spike on the Bank 1 O2 during the miss
  • Check-engine light flashes under load when misfire rate is severe
  • Cylinder-1 plug shows carbon fouling or oil bridging the insulator

Likely causes

  • Failed coil-on-plug or cracked boot on cylinder 1
  • Worn, fouled, or wrong-gap spark plug in cylinder 1
  • Low compression from burned valve or ring wear on cylinder 1
  • Injector stuck closed or electrically open on cylinder 1
  • Oil in the spark-plug well shorting the coil secondary

Recommended checks

  1. 1

    Swap cylinder-1 coil and plug with another cylinder and retest

  2. 2

    Run relative compression or leak-down focused on cylinder 1

  3. 3

    Scope coil primary current and injector current on cylinder 1

  4. 4

    Clear oil from the plug well and reseal the valve cover gasket

  5. 5

    Replace only the parts that move the misfire counter after swaps

DIY vs professional

DIY-safe: swap the cylinder-1 coil/plug with another cylinder and clear oil from the well. Pro: leak-down, injector balance, or valve work if the miss stays on the hole.

See also

Related terms

Content reviewed by a heavy-duty technician. About our editorial approach