P0301 — Cylinder 1 Misfire

Symptoms drivers report

• ▸A rhythmic shake at idle felt through the steering wheel and seat, often described as loping.
• ▸Loss of power that is most obvious pulling away from a stop or climbing a hill.
• ▸A flashing check engine light while the misfire is occurring.
• ▸A popping or puffing sound from the tailpipe at idle.
• ▸A raw gasoline smell at the exhaust.
• ▸Fuel economy down 10 to 20 percent on a four-cylinder, noticeably less on a V8.

What triggers this code

1. 1

   Failed ignition coil on cylinder 1

   Very common

   Coil-on-plug ignition puts a small transformer directly on top of each spark plug, in one of the hottest places on the engine. Insulation breaks down, the boot carbon-tracks, and the spark starts jumping to ground instead of across the plug gap. This is the most common single-cylinder misfire cause on any modern engine and the cheapest to test for.

   How to spot it

   Swap the cylinder 1 coil with the coil from cylinder 2. If the code becomes P0302 on the next drive, the coil is the fault.

   The fix

   Replace the coil, and replace that cylinder's spark plug at the same time — a weak coil almost always leaves a fouled plug behind.

   $80–$300•DIY friendly
2. 2

   Worn, fouled or cracked spark plug in cylinder 1

   Very common

   A plug whose gap has opened past specification needs more voltage than the coil can reliably supply, especially under load. Plugs also foul with oil from a leaking valve stem seal or with fuel from a dribbling injector, and a cracked porcelain insulator lets spark leak to ground before it ever reaches the gap.

   How to spot it

   The plug pulled from cylinder 1 looks visibly different from the others — sooty black, oil-wet, gap well past spec, or a hairline crack in the insulator.

   The fix

   Replace the plug with the manufacturer-specified type, gapped correctly. If it is oil-fouled, find where the oil is coming from before it happens again.

   $40–$250•DIY friendly
3. 3

   Clogged or failed fuel injector on cylinder 1

   Common

   An injector that has partially clogged sprays a poor pattern or too little fuel, and one with a failed winding does not open at all. Direct-injection engines add a second failure mode — carbon buildup on the injector tip — that produces the same code.

   How to spot it

   Coil and plug swaps do not move the code. A stethoscope on the injector shows cylinder 1 clicking differently or not at all, or its coil resistance is out of spec against its neighbors.

   The fix

   Bench-clean and flow-test the injector if it is only restricted, or replace it. Replace the seals whenever an injector is disturbed.

   $200–$600•Advanced DIY
4. 4

   Vacuum or intake leak feeding cylinder 1

   Occasional

   A leaking intake manifold gasket at one runner, or a cracked vacuum port near cylinder 1, admits unmetered air to that cylinder only. It runs lean while the others run normally, so the computer names one cylinder even though the fault is in the air side rather than the ignition side.

   How to spot it

   A short spray of carburetor cleaner or a propane wand near the cylinder 1 intake runner momentarily changes idle speed, and long-term fuel trim is high at idle.

   The fix

   Smoke-test the intake, then replace the intake manifold gasket or the cracked vacuum line.

   $100–$500•Moderate DIY•p0171
5. 5

   Low compression in cylinder 1

   Occasional

   A burnt exhaust valve, a worn valve seat, broken piston rings or a head gasket leaking between the cylinder and a coolant passage all reduce the cylinder's ability to compress. Spark and fuel are irrelevant if the mixture is not being squeezed. This is the expensive branch, and it is why a compression test belongs before the third parts purchase, not after.

   How to spot it

   A compression test shows cylinder 1 more than 15% below its neighbours. If adding a teaspoon of oil through the plug hole raises the reading, the rings are worn; if it does not, the fault is a valve or a head gasket.

   The fix

   Leak-down test to locate the loss, then a valve job, head gasket replacement or engine repair as required.

   $800–$4,000•Shop recommended

How to diagnose it

1. 1

   Confirm which cylinder is number 1 on your engine

   Cylinder 1 is not always the one nearest the front of the car. On most transverse four-cylinders it is at the end away from the transmission, on the passenger side. On Ford modular V8s it is the front-most cylinder on the passenger bank; on GM small-block V8s it is the front-most on the driver bank. Get this wrong and you replace a perfectly good coil while the bad one stays in the engine. Check the service information for your specific engine before you touch anything.

   Result: Prevents the most common wasted repair on this code.

2. 2

   Read the freeze frame before clearing anything

   Note engine speed, calculated load and coolant temperature from when the code set. A misfire only at cold idle points at plugs, coils or a stretched chain. A misfire only under high load points at fuel delivery or a coil breaking down under cylinder pressure. This decides how you test.

   Tools: OBD-II scan tool with freeze-frame support

   Result: Tells you which conditions to reproduce.

3. 3

   Do the coil swap test

   Move the cylinder 1 coil to cylinder 2 and the cylinder 2 coil to cylinder 1. Clear the code, drive until the light returns, then rescan. P0302 means the fault followed the coil and the coil is bad. P0301 still means the coil is fine and the problem stays with the cylinder. This test costs nothing and settles the most likely cause outright.

   Tools: Socket set, OBD-II scan tool

   Result: Confirms or eliminates the ignition coil for free.

4. 4

   Pull the plug and read it against its neighbours

   Remove the cylinder 1 plug and one other for comparison. A light tan tip is normal. Dry black soot means a rich mixture or a weak spark. Oily and wet means oil is entering the cylinder past rings or valve seals. Wet with fuel means the injector is delivering but nothing is igniting it. A white or blistered tip means the cylinder has been running too lean and hot.

   Tools: Spark plug socket, Extension and ratchet

   Result: Turns a code into physical evidence about what is happening inside that cylinder.

5. 5

   Test the injector if the coil and plug are cleared

   Listen to each injector with a stethoscope or a long screwdriver against your ear — the ticking should be identical across cylinders. Then measure resistance across the injector terminals and compare with the others; a reading more than about 10% off is suspect. On some engines you can also swap the cylinder 1 injector with a neighbour and see whether the code follows, exactly as with the coil.

   Tools: Mechanic's stethoscope, Digital multimeter, Noid light

   Result: Identifies a fuel delivery fault confined to one cylinder.

6. 6

   Compression and leak-down test

   If ignition and fuel are both proven good, the cylinder is not sealing. A compression test gives you the number; a leak-down test tells you where the pressure is going. Air out the tailpipe means an exhaust valve, air out the intake means an intake valve, air out the oil filler means rings, bubbles in the coolant means a head gasket.

   Tools: Compression tester, Leak-down tester, Air compressor

   Result: Locates the mechanical failure precisely before any teardown is quoted.

Repairs & cost

Vehicles that set this code often

Design details that make some models more prone to this fault than others.

• Nissan Altima

  QR25DE ignition coils fail individually and repeatedly, so an Altima owner often sees P0301 followed by a different cylinder's code within a year. Because the coils are sitting exposed on top of the engine and are inexpensive, replacing the full set is a common and reasonable choice here.

• Honda Civic

  1.5-liter turbo Civics are known for fuel diluting the engine oil in cold-climate short-trip use. The resulting fouling produces single-cylinder misfires that clear up once the engine reaches full temperature, which sends people chasing coils when the real problem is the duty cycle the car is being used for.

• Toyota Corolla

  Coils on the 2ZR-FE are unusually durable, so a P0301 on a Corolla more often traces to an iridium plug left in past its 120,000-mile interval than to an ignition failure. Check plug mileage before ordering a coil on this engine.

• Jeep Grand Cherokee

  The 3.6-liter Pentastar V6 in early 2011–2013 vehicles had a documented cylinder head problem where a valve seat wore and dropped compression on an individual cylinder. On these, a misfire that does not follow a swapped coil deserves a compression test before more parts are bought.

• 2021 BMW 3 SeriesOn the B58 inline-six, a single-cylinder misfire is most often an ignition coil, and swapping the coil to an adjacent cylinder to see whether the misfire follows is the fastest free diagnostic. If it does not move, look at the direct injector for that cylinder — BMW injectors are individually coded and a replacement must be coded to the engine control unit.
• 2021 Chevrolet Silverado 1500Cylinder-specific misfires on these V8s cluster on the cylinders the deactivation system uses most heavily. A repeated single-cylinder code on a truck past 70,000 miles is a stronger lifter indicator than a random misfire alone.
• 2021 Ford F-150Cylinder 1 misfire on the 5.0L is most often a failed coil-on-plug. Ford's coils are individually replaceable and inexpensive; replacing all eight at once is common practice past 100,000 miles.
• 2019 Ford F-150On the 3.5L and 2.7L EcoBoost, a single-cylinder misfire usually means the coil-on-plug boot has failed or the plug gap has opened past spec — turbocharged cylinder pressure is far less forgiving of a worn plug than a naturally aspirated engine, which is why EcoBoost plugs are a 60,000-mile item rather than 100,000.
• 2021 Honda AccordA cylinder-1 misfire on the 1.5L is worth cross-checking against the dipstick — badly fuel-diluted oil and a wet plug point to the dilution issue rather than a failed coil. On the 2.0L turbo, a single-cylinder misfire under boost is more often an injector than a coil.
• 2021 Honda CivicCylinder 1 misfire on the 1.5T is usually a failed ignition coil or a plug fouled by diluted oil. On a cold-climate short-trip car, check the oil level and smell before replacing parts — dilution and misfire are frequently the same story.
• 2019 Honda CivicA cylinder-1 misfire on a turbo Civic is worth taking seriously because heavily fuel-diluted oil and a fouled plug produce exactly this. Pull the plug and look at it: fuel-wetted plugs alongside a high oil level tie the misfire back to the dilution issue rather than a failed coil.
• 2021 Kia SportageA single-cylinder misfire on a Theta II engine deserves more attention than on most vehicles. Check the plug and coil first, but if the misfire is accompanied by any knocking noise or by oil consumption, have the bearing condition assessed before you spend money on ignition parts.

Finding cylinder 1 on your engine

The coil swap test, step by step

Frequently asked questions

Related information