P0301: Cylinder 1 Misfire Detected (and P0302–P0306)
P0301 is one of the friendlier codes you can get, strange as that sounds, because it does half the diagnostic work for you. The computer isn't just saying the engine misfires; it's naming the cylinder. Everything on this page applies equally to P0302 through P0306, where the final digit is simply the cylinder number. A separate article for each would tell you nothing new, so we've kept the family together.
What P0301 actually means
The crankshaft sensor watches for the small kick each cylinder's combustion delivers. When cylinder 1 repeatedly fails to deliver its kick, the computer stores P0301: Cylinder 1 Misfire Detected. Which physical cylinder is number 1 varies by engine layout, so check your car's firing order diagram before pulling anything apart; on plenty of engines it is not the one nearest the front of the car.
Can you keep driving?
Severity: 4 out of 5 flashing, 3 out of 5 steady. The flashing-light rule from P0300 applies here word for word: a flashing lamp means stop, because raw fuel from the dead cylinder is cooking the catalytic converter. A steady lamp buys you a few gentle days to run the test below.
What causes P0301 (most likely first)
- The ignition coil on cylinder 1. On coil-on-plug engines, a single failed coil is the textbook cause of a single-cylinder misfire.
- The spark plug in cylinder 1. Fouled, cracked, or simply worn past its gap.
- The injector on cylinder 1. Clogged or electrically dead. Less common than ignition, and it announces itself by surviving the swap test below.
- Low compression in that cylinder. A burnt valve, damaged rings or a head gasket breach. The expensive tier, confirmed by a compression or leak-down test rather than guessed at.
- A wiring or connector fault. A chafed coil harness or corroded plug does everything a dead coil does, for the price of a repair to the loom.
The free test that solves most of these
Swap the cylinder 1 coil with a neighbouring cylinder's coil. Clear the code. Drive. If the misfire moves to the neighbour, becoming P0302 or whichever cylinder you chose, the coil is guilty and you've diagnosed the fault for the cost of ten minutes and a socket set. If the misfire stays on cylinder 1, the coil is innocent and attention shifts to the plug, then the injector, then compression. Workshops run exactly this test; there's no reason you can't.
Symptoms you'll notice
A steady rhythmic shudder at idle, like the engine has a limp. Down on power, worse fuel economy, and sometimes a fuel smell at the tailpipe. One dead cylinder on a four-cylinder is a quarter of the engine gone, and it feels like it.
What it costs to fix in Australia
| Repair | Typical cost (AUD) |
|---|---|
| Single coil, fitted | $150–350 |
| Spark plug set, fitted | $150–400 |
| Single injector, fitted | $250–600 |
| Compression test | $120–250 |
| Valve or head repair | $1,500–4,000+ |
Replace plugs as a set even when only one cylinder misfires. Fitting one fresh plug next to three tired ones just books the next misfire in advance.
P0301 on Australian cars
The same suspects as the random-misfire code, with sharper focus: individual Falcon and Commodore coils, Hyundai and Kia coil-on-plug units that die one at a time, and Camrys whose oil use fouls one plug before the others. Diesel utes largely sit this one out; single-cylinder codes on a HiLux or Ranger point toward injectors and are a different conversation, covered under P0087 territory.
Will P0301 fail rego or a roadworthy?
The lamp fails a NSW pink slip on cars over five years old and a sale-time certificate in Victoria or Queensland. An examiner can also feel a single-cylinder miss at idle from the driver's seat, so this isn't a code that hides well in person.
How to read and clear P0301
Read the code, run the coil swap, and use live misfire counters to confirm the fix; watching the cylinder 1 counter sit at zero after the repair is more reassuring than waiting to see whether the lamp returns. Other codes are indexed in the fault code library.
P0301 FAQ
What do P0302, P0303 and the rest mean?
The identical fault on a different cylinder: P0302 is cylinder 2, P0303 is cylinder 3, through to P0306. Diagnosis is the same swap-and-track process aimed at whichever cylinder is named.
Which cylinder is number 1?
It depends on the engine. Check the firing order for your specific model before assuming; guessing wrong wastes the whole swap test.
Can I drive with a cylinder 1 misfire?
Gently and briefly with a steady lamp, not at all with a flashing one. The catalytic converter pays for every kilometre of active misfire.
Why does my misfire only happen when it rains?
Moisture finding a cracked coil boot or worn plug lead. Damp-morning misfires that clear by lunchtime are an ignition insulation fault nearly every time.
Related codes: P0300 · P0420 · P0171 · Full fault code library
A fault code is a starting point, not a diagnosis. The same code can have different causes on different vehicles, and any costs shown are typical Australian ranges only. Always have the fault confirmed by a qualified mechanic before buying parts or booking repairs.