Cylinder Misfire by Number (P0301–P0308): The Complete Guide
Eight codes, one diagnosis logic. Here's the version of the cylinder-misfire story that doesn't change for each digit.
P0301 through P0308 are some of the most-Googled engine codes for a reason: they're scary, they're cylinder-specific, and they all share the same diagnosis logic. This guide consolidates everything you need to know about cylinder-specific misfire codes in one place — what each code means, how to figure out which physical cylinder is involved on your engine, the swap-test diagnosis flow, and when a misfire stops being safe to drive on.
What each P030X code actually says
Every code in the P0301–P0308 family says exactly one thing: cylinder N misfired enough during a recent drive cycle to fall outside the ECM's acceptable threshold. The X digit is the cylinder number. P0301 is cylinder 1, P0308 is cylinder 8. There is no extra information encoded in the code beyond which cylinder.
What the ECM actually measures is crankshaft speed. Every combustion event accelerates the crankshaft slightly; the ECM watches for the expected acceleration after each cylinder fires. When a cylinder skips, the crankshaft doesn't get its expected push, and the deviation gets logged against that specific cylinder. This is why misfires are detected without a dedicated misfire sensor — the crankshaft position sensor doubles as the detector, per the SAE J2012 standard governing generic OBD-II powertrain codes.
Figuring out which physical cylinder is "cylinder N" on your engine
The OBD-II standard says nothing about which physical cylinder gets the number 1. That's the manufacturer's call, and it varies by engine family — sometimes within the same brand. Get this wrong and you'll swap a coil on the wrong cylinder, fix nothing, and chase a phantom failure.
Inline-4 engines
Almost universally, cylinder 1 is at the timing-belt/chain end of the engine. On transverse FWD layouts (the vast majority of modern compact and midsize cars), that's the passenger side of the engine bay in North America and the driver side in the UK / Australia.
| Code | Cylinder position | Notes |
|---|---|---|
| P0301 | 1 (front, timing-belt/chain end) | Front-most cylinder on the block. Easy access on most transverse FWD layouts. |
| P0302 | 2 | Middle-front. Often runs the hottest pair with cyl 3 due to lower airflow. |
| P0303 | 3 | Middle-rear. Same thermal stress as cyl 2. |
| P0304 | 4 (rear, flywheel/transmission end) | Rear-most cylinder. Slightly cooler than middle cylinders. |
V6 engines
Cylinder numbering on V6 engines depends on the engine family. Toyota's 2GR-FE numbers bank 1 (which contains cylinders 1, 3, 5) on the rear side. Honda's J35 numbers bank 1 (cylinders 1, 2, 3) on the front side. Always confirm bank 1 versus bank 2 for your engine code before buying parts.
| Code range | Cylinders | Notes |
|---|---|---|
| P0301 – P0303 | Cylinders 1, 2, 3 (Bank 1) | Bank 1 is the bank containing cylinder 1 — manufacturer-specific. Often the front bank on transverse V6 (closest to firewall on Toyota, opposite on Honda). |
| P0304 – P0306 | Cylinders 4, 5, 6 (Bank 2) | The opposite bank. Confirm your engine's Bank 1/Bank 2 designation in the factory service manual. |
V8 engines
V8s are where conventions get fragmented. Ford's "modular" V8 family (4.6L, 5.4L, 5.0L Coyote) numbers passenger side 1-2-3-4 and driver side 5-6-7-8. GM's LS family does the opposite. Chrysler HEMI yet another convention. Cross-reference the FSM.
| Code range | Cylinders (typical) | Notes |
|---|---|---|
| P0301 – P0304 | Cylinders 1–4 (typically Bank 1) | On Ford "Modular" V8, bank 1 is passenger side. On GM LS V8, bank 1 is driver side. |
| P0305 – P0308 | Cylinders 5–8 (typically Bank 2) | Opposite bank. Critical to confirm convention for your specific engine family before parts shopping. |
P030X at-a-glance: severity, cost, and what to expect
| Dimension | Value |
|---|---|
| Code range | P0301 – P0308 (some heavy-duty engines extend to P0312) |
| OBD-II type | Generic powertrain (P0), SAE J2012 defined |
| Set criteria | ECM detects per-cylinder crankshaft speed variation outside threshold during a drive cycle |
| CEL behavior | Steady = misfire logged but not active. Flashing = active misfire damaging catalyst right now. |
| Severity (steady) | Medium — diagnose within a few drive cycles |
| Severity (flashing) | Critical — reduce load, get off the road as soon as safe |
| Common cost (DIY) | $20 – $60 (spark plug) up to $150 (coil) |
| Common cost (shop) | $150 – $600 depending on cylinder accessibility and parts |
| Worst-case cost | $1,000 – $2,500+ if catalyst is destroyed by sustained misfire |
The 5-step diagnosis flow (works on every P030X code)
The diagnosis order doesn't change based on which cylinder is misfiring. It changes based on the engine's age, mileage, and whether the misfire is constant or intermittent. The cheapest, most-replaceable component first; mechanical issues last.
Step 1
Confirm the exact cylinder
Read the code with an OBD-II scanner or the STEER app. P0301 = cylinder 1, P0302 = cylinder 2, P0303 = cylinder 3, P0304 = cylinder 4, P0305 = cylinder 5, P0306 = cylinder 6, P0307 = cylinder 7, P0308 = cylinder 8. Cross-reference the cylinder number against your factory service manual diagram for your engine code (e.g. 2.0L K20 vs 2.0L EA888 are numbered differently).
Step 2
Inspect the spark plug
Pull the spark plug from the misfiring cylinder and compare it to the others. A normal plug is tan-gray. A wet/oily plug suggests oil consumption or a leaking valve cover gasket. A white/blistered plug means the cylinder is running lean or too hot. A black, fouled plug points to a rich condition or a failed coil. Re-gap to manufacturer spec and reinstall.
Step 3
Run the swap test
Move the ignition coil from the misfiring cylinder to an adjacent cylinder. Clear the code and drive 5–10 minutes. If the misfire follows the coil to the new cylinder, replace the coil. If the misfire stays on the original cylinder, the coil is fine — move to step 4.
Step 4
Test the fuel injector
With the engine running, listen at each injector with a long screwdriver as a stethoscope. Each injector should click rhythmically. A silent injector is open-circuit; an erratic click points to a partially clogged or failing injector. Resistance testing across the injector pins should match manufacturer spec (typically 11–17 ohms for high-impedance injectors).
Step 5
Check compression if everything else passes
If spark and fuel are confirmed good and the misfire persists, perform a compression test on the misfiring cylinder. A reading more than 10–15% below the other cylinders indicates a mechanical issue — worn rings, burned valve, or head gasket failure. This is the point where the repair moves from driveway DIY to professional shop.
When a misfire becomes catalyst-damaging
A misfiring cylinder dumps unburned fuel and oxygen into the exhaust. When that mixture reaches the catalytic converter (operating at 800°C+), it ignites inside the catalyst, raising local temperatures past 1,200°C and melting the ceramic substrate. Once the substrate is melted, the catalyst is permanently destroyed — and on most modern vehicles, that's a $1,000 to $2,500 component.
The flashing check engine light is the ECM's way of telling you this is happening right now. Reduce load, avoid acceleration, and stop driving as soon as it's safe. The EPA's federal emissions warranty (8 years / 80,000 miles on the catalyst for most light-duty vehicles) doesn't cover damage caused by driving with a known active misfire.
Related codes and where to read next
If multiple cylinders are misfiring simultaneously, the ECM will log P0300 (random/multiple misfire) instead of a numbered P030X. P0300 alongside a P030X code means "cylinder N is misfiring badly enough that the random-misfire threshold has also been crossed." Diagnose the numbered code first; P0300 typically clears once the specific cylinder is fixed.
Misfires that only appear under specific conditions get covered separately: idle-only misfires, load-only misfires, and post-service misfires have different fault profiles than a constant cylinder-specific misfire.
Frequently asked questions
What is the difference between P0300 and P0301–P0308?+
P0300 is a random or multiple-cylinder misfire — the engine control module (ECM) sees misfires happening across more than one cylinder and can't isolate a single source. P0301 through P0308 are cylinder-specific codes: P0301 is cylinder 1, P0302 is cylinder 2, and so on through P0308 (cylinder 8). The ECM uses small variations in crankshaft speed to figure out which cylinder skipped a combustion event, which is why a single-cylinder misfire produces a numbered code.
How do I know which cylinder is "number 1" on my engine?+
Cylinder 1 is defined by the manufacturer, not the OBD-II standard. On most inline-4 and inline-6 engines, cylinder 1 is at the front of the engine (timing belt or chain end). On a transverse V6 or V8, cylinder 1 is typically the front-bank cylinder closest to the timing cover. On longitudinally mounted V-engines (RWD), it varies — Ford typically numbers passenger-side bank as 1-2-3-4 and driver-side as 5-6-7-8, while GM small-block V8s use a different convention. Always cross-reference your factory service manual or a manufacturer-specific diagram for your engine code.
Is a single-cylinder misfire serious?+
It depends on whether the check engine light is flashing. A steady light (P0301–P0308 logged) means a misfire was detected but is no longer continuous — you can usually drive at low load to a shop. A flashing check engine light means an active misfire is dumping unburned fuel into the exhaust right now, which superheats and can destroy the catalytic converter within minutes. Reduce speed, avoid acceleration, and get the car off the road as soon as it's safe.
What is the "swap test" and does it really work?+
The swap test is the cheapest, fastest way to diagnose a single-cylinder misfire. You move the ignition coil (or spark plug) from the misfiring cylinder to a known-good cylinder, clear the code, and drive. If the misfire follows the part (e.g. P0301 becomes P0303), the coil or plug is the problem. If the misfire stays on the original cylinder, the cause is downstream — a fuel injector, valve, or compression issue. It works because most single-cylinder misfires are caused by the cheapest, most-replaceable components first.
Why does my car only misfire on one specific cylinder?+
Because that cylinder's spark, fuel, or compression is uniquely degraded. Spark plugs and ignition coils don't always fail uniformly — heat, oil leakage past valve cover gaskets, and even cylinder position within the engine block (cylinders in the middle of an inline-4 often run hotter) can cause one cylinder to wear faster. If one cylinder consistently misfires across multiple part swaps, the underlying issue is usually compression-related: worn valve seats, a burned exhaust valve, or piston ring wear.
Can I drive with a P0301 code if the light is steady?+
A steady light gives you a margin, not permission. You can usually drive short distances at low speed (no highway, no hills, no heavy acceleration) to get to a shop or pick up parts. The risk increases with time and load: a misfire that becomes continuous (flashing light) can destroy a catalytic converter, which is the most expensive component the misfire threatens. Diagnose within a few drive cycles, not a few weeks.
Does cylinder number affect the diagnosis approach?+
Slightly. On inline-4 engines, the middle cylinders (2 and 3) run hotter than the end cylinders (1 and 4), which means cylinder 2 and 3 misfires are sometimes thermal-stress patterns. On V6 and V8 engines, the cylinder number tells you which bank you're working on — and on rear banks of transverse-mounted V6s, the physical access is often the deciding factor in whether you swap-test in your driveway or hand it to a shop. The diagnosis logic (spark → coil → injector → compression) doesn't change, only the geometry of the work does.
Reviewed by Albert Carles, Hardware Engineer, OBD-II Specialist. STEER provides diagnostic information, not professional inspection. For active misfires (flashing check engine light), stop driving and contact a qualified mechanic.
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