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P0301 code: misfire in cylinder 1

Fault code P0301 means the engine control module has detected misfires in cylinder 1. The air-fuel mixture in that cylinder does not burn properly, so the engine shakes and loses power. Because the fault is limited to one cylinder, the cause is often a single part: the spark plug, ignition coil or injector for that cylinder.

Check P0301

When the code is set

The ECM uses the crankshaft position sensor to monitor how evenly the crankshaft turns. When cylinder 1 misfires, the crankshaft slows for a moment at a precise point, so the ECM knows which cylinder is misfiring. When there are too many misfires, it stores P0301; with severe misfires the check engine light flashes. The manufacturer decides which cylinder is number 1, so a mechanic looks it up in the data for your engine.

Can I keep driving?

Have it checked soon

If the check engine light flashes, stop when it is safe and do not drive on: unburnt fuel can destroy the catalytic converter. If the light stays on steadily and the engine runs almost normally, drive gently without hard acceleration and have the car checked as soon as possible. If the engine shakes badly or loses power, it is better to have it taken to a garage.

Symptoms

  • The check engine light is on or flashing.
  • The engine shakes, especially at idle.
  • Jerking and less power when accelerating.
  • Hard starting.
  • Higher fuel consumption.

Common causes

  • A worn or fouled spark plug in cylinder 1.
  • A faulty ignition coil or spark plug lead on cylinder 1.
  • A clogged or faulty injector on cylinder 1.
  • An air leak at the cylinder 1 intake port.
  • Low compression in cylinder 1, for example from a damaged valve.

How to find the cause

A mechanic usually works like this:

  1. Read all stored codes and freeze frame data.
  2. Inspect the cylinder 1 spark plug and replace it if needed; if the plugs are old, replace them all.
  3. Swap the cylinder 1 coil with the one from a neighbouring cylinder. If the fault moves (for example to P0302), the coil is to blame.
  4. If the fault stays in cylinder 1, check that cylinder’s injector.
  5. If ignition and fuel are fine, run a compression test.

Other ways the code is written

Scan tools and workshop printouts sometimes show the code with extra characters:

  • P030100

Related codes

Frequently asked questions

Evoca fault code diagnostics is an informational aid and does not replace a professional inspection of your vehicle. Only an inspection of the vehicle at a workshop can confirm the cause of a fault.

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