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P codepowertrainHigh severity

P0314Single Cylinder Misfire (Cylinder not Specified)

The engine computer has detected a misfire in one cylinder but cannot determine which cylinder is misfiring.

Definition

The PCM detects misfires by measuring tiny variations in crankshaft acceleration between firing events; when it sees a single-cylinder misfire pattern but cannot attribute it to a specific cylinder — often because camshaft/crankshaft correlation data is unavailable or degraded — it sets P0314 instead of a P0301-P0312 code. Expect a rough idle, hesitation, and shaking under load, with the MIL on steady or flashing when the misfire rate threatens the catalytic converter. Sustained misfiring dumps raw fuel into the exhaust and can overheat and destroy the catalyst, so this code should not be driven on indefinitely.

Common causes

  • Worn or fouled spark plug on one cylinder
  • Failing ignition coil or coil boot
  • Restricted, leaking, or stuck fuel injector
  • Vacuum leak affecting one cylinder (intake gasket, cracked runner)
  • Low compression from a burned valve, worn rings, or a lifter/cam lobe failure
  • Degraded crankshaft/camshaft sensor signal preventing cylinder identification

Common misdiagnoses

  • All plugs and coils replaced when only one cylinder is at fault
  • Fuel pump replaced for a single-cylinder fuel delivery issue
  • Catalytic converter replaced for symptoms the misfire itself caused
  • MAF or O2 sensors replaced for fuel-trim shifts that are a consequence, not the cause

Troubleshooting steps

  1. 1.Pull freeze frame and Mode 6 misfire counters

    Many PCMs still record per-cylinder misfire counts in Mode 6 even when the stored code is P0314 — that data often identifies the offending cylinder directly.

  2. 2.Check for cam/crank sensor codes

    P0315, P0335-P0340 series faults explain why the PCM could not assign the misfire to a cylinder; repair those first.

  3. 3.Isolate the cylinder mechanically

    Use a power-balance test or disable injectors one at a time with a scan tool — the cylinder with no RPM drop when killed is the misfiring one.

  4. 4.Swap the coil and plug to adjacent cylinders

    If the misfire count follows the moved part, replace that coil or plug; inspect the plug for oil, coolant, or carbon fouling as a clue to deeper problems.

  5. 5.Test fuel delivery to the suspect cylinder

    Compare injector resistance (typically 11-16 Ω for saturated injectors) and run an injector balance test to catch a restricted or dead injector.

  6. 6.Run compression or leak-down if ignition and fuel check out

    Cylinders should be within about 10-15% of each other; a low cylinder points to valves, rings, or a valvetrain (lifter/cam) failure.

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