P0301 Code: Cylinder 1 Misfire Detected

What happens if you don't fix it

Symptoms you can actually notice

• Shaking at idle
• Loss of power
• Flashing light under load

What the computer is actually complaining about

The crank sensor detects a slight slowdown each time cylinder 1 fails to burn its charge. The computer logs that stumble against cylinder 1 alone rather than the whole engine. Once the count crosses a threshold in a single drive cycle, it stores P0301 and turns on the light.

Most likely causes, cheapest check first

What you need in your hands

• OBD-II scanner with misfire counters

  Any $25 Bluetooth reader plus a free phone app shows the per-cylinder misfire count on most cars built after 2010.

• Spark plug socket Optional

  A 5/8 inch socket with a rubber insert runs about $8 and holds the plug so it does not drop into the well.

• Compression gauge Optional

  $25 to $40 at a parts store. Screws into the plug hole and reads cylinder pressure in PSI.

Test it yourself, step by step

Do these in order. Each step tells you what to do, what to look at, what counts as fine, what counts as broken, and what you will actually see.

1. 1 Plug the scanner into the trapezoid port under the dash on the driver side, above your left knee. Idle the engine and open the misfire counter screen.

   Look at

   The counter for cylinder 1 compared with its neighbors while the engine idles and again at 2000 rpm.

   Fine if

   Cylinder 1 counts no higher than any other cylinder across two minutes of idling.

   Broken if

   Cylinder 1 climbs while the others hold at zero. A count that rises only at higher rpm points at ignition or fuel rather than compression.

   What you'll see One number ticking upward while the rest sit still. That single number is your whole diagnosis.

2. 2 Open the hood and find cylinder 1, which sits at the front of the engine on a transverse layout, nearest the passenger side belt drive.

   Look at

   The coil pack and plug boot on cylinder 1 for a burnt smell, a cracked body, or oil pooled in the well.

   Fine if

   A clean coil body seated flush with a dry plug well.

   Broken if

   Oil standing in the well or a coil with a melted base. Oil shorts the plug and sets this code on its own.

   What you'll see A coil identical to its neighbors. Any difference in color or smell marks it as suspect.

3. 3 Swap the cylinder 1 coil with the coil from cylinder 2 along the top of the valve cover, then drive about 20 miles and reread the counters.

   Look at

   Whether the misfire counter now sits on cylinder 2 instead of cylinder 1.

   Fine if

   The misfire stays on cylinder 1, which clears the coil and shifts suspicion to the injector or the valve sealing.

   Broken if

   The misfire follows the coil to cylinder 2. That coil is faulty and the swap has proven it.

   What you'll see The counter either stays or moves. Both outcomes cut the list of suspects in half.

4. 4 Pull the cylinder 1 spark plug with the 5/8 inch socket and hold it beside the plug from cylinder 2.

   Look at

   Electrode color, gap width, and whether the plug tip is wet with fuel or oil.

   Fine if

   A light tan tip with a sharp edge and a gap within a few thousandths of the factory figure.

   Broken if

   A black wet tip, a rounded electrode, or a gap visibly wider than the neighbor's plug.

   What you'll see Two plugs side by side. The difference is obvious once they are out of the engine.

5. 5 Screw the compression gauge into the cylinder 1 plug hole under the hood and crank the engine for four compression strokes with the throttle held open.

   Look at

   The peak pressure reading, then repeat the same test on cylinder 2 for comparison.

   Fine if

   Cylinder 1 reads within 10 percent of cylinder 2 and above roughly 120 PSI on a warm engine.

   Broken if

   Cylinder 1 reads more than 15 percent lower than its neighbor. That points at a valve or ring problem, and no ignition part will fix it.

   What you'll see A needle that jumps on each stroke and settles. A low first stroke that barely rises means the cylinder is not sealing.

What the repair costs

Reference range compiled from 2 source type(s), as of 2026-11. This is not a quote — actual cost depends on your vehicle, region, and which part turns out to be the real cause.

Basis: reference · 2 source types cross-checked · Data as of 2026-11 · Confidence: medium

How to confirm it's really fixed

✓ Clear the code and drive two complete warm-up cycles, including one highway stretch. If the cylinder 1 counter stays at zero through both, the repair held. If the count returns, move on to the injector before replacing anything else.

Common questions