P0301 · P0302 · P0303 · P0304 · P0305 · P0306 · P0307 · P0308
Cylinder Misfire Detected
P0301–P0308
A P030x code means the PCM has detected a misfire on a specific cylinder — the number at the end tells you exactly which one. The coil swap test is the fastest and cheapest way to isolate the cause, and it costs nothing to perform.
// 01 — Which Code, Which Cylinder
P0301–P0308 — What the Number Means
The last digit identifies the misfiring cylinder by number. Cylinder numbering follows the manufacturer’s convention — not necessarily physical position. Always consult your specific engine’s cylinder numbering diagram before testing.
Code → Cylinder Reference
Cylinder 1 is almost always the front cylinder on the timing-chain/belt end of the engine
P0301
Cylinder 1
Timing end — usually front-left on inline engines
P0302
Cylinder 2
Second from timing end
P0303
Cylinder 3
Third — middle on 4-cyl engines
P0304
Cylinder 4
Rear on 4-cyl · fourth on 6/8-cyl
P0305
Cylinder 5
V6/V8/I5 engines only
P0306
Cylinder 6
V6 rear cylinder · V8 sixth
P0307
Cylinder 7
V8 engines only
P0308
Cylinder 8
V8 rear cylinder
P0301 alongside P0300? A specific cylinder code (P0301) alongside the random misfire code (P0300) is normal — P0300 fires whenever the misfire rate across any cylinder exceeds the threshold. Both codes being present doesn’t mean two separate faults. Fix the cylinder-specific code first and P0300 will clear with it.
// 02 — Immediate Decision
Drive or Park?
⚡
The check engine light behaviour is the deciding factor
// Stop Driving Now
CEL is flashing — active misfire destroying the catalytic converter right now
Engine shaking severely — whole cabin vibrating
Fuel smell or visible exhaust smoke alongside misfire
Temperature gauge rising above normal
Engine sounds like it may stall at any moment
// Drive Carefully to Shop
CEL is solid (not flashing) — fault stored but not currently active
Slight rough idle or mild stumble only
Normal temperature, no smoke, no stalling
Misfire only under specific conditions (cold, load)
Avoid sustained highway speed until diagnosed
Flashing CEL + misfire = active catalyst damage. Every second at highway speed with a severe misfire pushes unburned fuel into the converter. At highway speed a severe misfire can destroy a $500–$2,500 catalytic converter in under 20 minutes. Pull over, reduce load, read the guide on the flashing CEL page →
// 03 — The Coil Swap Test
The Coil Swap Test — Free, 10 Minutes, Definitive
A cylinder-specific misfire code points to one cylinder — but it doesn’t tell you whether the fault is in the coil, the plug, the injector, or the cylinder itself. The coil swap test isolates the coil for free in one step. It is always the correct first test on any COP (coil-on-plug) engine when a cylinder-specific misfire is stored.
Coil Swap Test — Step by Step
Works on all coil-on-plug (COP) engines — most vehicles made after 2000
1
Note the stored code and identify the misfiring cylinder
P0301 = Cylinder 1. P0304 = Cylinder 4. Find that cylinder on the engine. On inline engines, cylinder 1 is at the timing-belt/chain end. On V-engines, Bank 1 is the side containing cylinder 1 — check your owner’s manual or a diagram for your specific engine layout.
2
Remove the coil from the misfiring cylinder
Disconnect the coil’s electrical connector. Remove the coil bolt (usually 8mm or 10mm). Pull the coil straight up from the plug well. Inspect the coil boot (the rubber tip) for cracks, carbon tracking, or white mineral residue — any of these confirm the coil boot is the leak path. If oil is present in the plug well, address the valve cover gasket before swapping coils.
3
Swap the suspect coil to a known-good cylinder
Take the coil from the misfiring cylinder (e.g. cylinder 1) and install it on an adjacent cylinder (e.g. cylinder 2). Move the coil from cylinder 2 to cylinder 1’s location. Now the coils are swapped. Reconnect all electrical connectors. The goal is to see if the misfire follows the coil to its new location.
4
Clear codes and drive for 5–10 minutes
Clear all stored codes with a scanner. Drive normally — ideally including the conditions that originally triggered the code (cold start, idle, light acceleration). Allow enough drive time for the PCM to detect any misfire on the new cylinder if the coil is bad. On most vehicles the misfire detection window is 200–400 engine revolutions — typically 2–3 minutes of driving is enough.
5
Read the new code — interpret the result
If the misfire code moved to the new cylinder (the cylinder the suspect coil is now on) — the coil is confirmed bad. Replace only that coil. If the misfire code stayed on the original cylinder — the coil is fine. The fault is in the spark plug, fuel injector, wiring, or the cylinder itself (compression). Proceed to checking the plug on that cylinder next.
Oil in the plug well changes the diagnosis. If you remove the coil and find oil in the plug well, the valve cover gasket is leaking. The oil attacks the coil boot rubber and will destroy new coils just as quickly. Fix the valve cover gasket first, clean the well, replace the coil — replacing the coil without fixing the oil leak is a temporary repair.
// 04 — Causes Ranked by Likelihood
5 Causes of a Cylinder-Specific Misfire — Ranked
The coil swap test separates cause #1 from everything else. If the misfire doesn’t follow the coil, work down this list on the original cylinder.
1
Failed Ignition Coil (COP engines)
Very Common
The single most common cause of a cylinder-specific misfire on modern COP engines. Coils fail in several ways: complete internal failure (no spark at all), heat-related breakdown (fires cold, fails when hot), moisture arcing through a cracked boot, and oil contamination from a leaking valve cover gasket. A failed coil produces a sudden, severe single-cylinder misfire — often the CEL comes on without warning mid-drive. The coil swap test is definitive and costs nothing. Replace with an OEM-specification coil — aftermarket coils have a noticeably higher early failure rate on many European and Japanese applications.
2
Worn or Fouled Spark Plug
Very Common
If the coil swap test shows the code stays on the original cylinder, the spark plug is the next check. A plug with a worn electrode (gap too wide), heavy carbon fouling (from rich running or oil consumption), or a cracked ceramic insulator will misfire on that cylinder regardless of how good the coil is. Remove the plug and inspect: a healthy plug has a light tan electrode with minimal deposits and a gap within spec. Oil-fouled plugs — black and oily — indicate an additional underlying problem (valve stem seals, piston rings) that needs addressing alongside the plug replacement.
3
Fuel Injector — Failed or Clogged
Common
A failed or severely clogged injector on one cylinder starves that cylinder of fuel — the coil fires but there’s nothing to ignite. The misfire code stays on the original cylinder after the coil swap test, and the plug is clean (not fouled, not worn) — because no fuel is reaching it to foul it. A companion P020x (injector circuit) code may be stored alongside the P030x. Injector failure is confirmed by testing resistance at the injector connector (should be 11–18 ohms on most petrol injectors) and by comparing the buzzing sound of each injector at idle with a mechanic’s stethoscope — a dead injector is silent when the others are clicking.
4
Wiring / Connector Fault — Coil or Injector Circuit
Moderate
The coil swap test swaps the coil but leaves the wiring harness in place. If the misfire stays on the original cylinder after a confirmed good coil is installed, and the plug and injector test fine, the fault is in the wiring or connector for that cylinder’s coil or injector circuit. Common failure points: corroded coil connectors (particularly on engines exposed to water intrusion), chafed wiring from a broken harness routing clip, or a failed PCM driver for that coil channel. Inspect the coil connector on the affected cylinder for corrosion, pushed-out terminals, or melted insulation.
5
Low Compression — Mechanical Cylinder Fault
Less Common
If the coil swap test doesn’t move the code, the plug is fine, the injector is working, and wiring checks out — do a compression test on the affected cylinder. A cylinder with significantly low compression (burned or bent valve, failed piston rings, damaged head gasket at that cylinder) will misfire regardless of what ignition or fuel components are on it — there isn’t enough compression to support combustion. All cylinders should be above 130 PSI and within 15% of each other. A leakdown test after a low-compression reading pinpoints where the compression is escaping (valves, rings, or head gasket).
// 05 — Step-by-Step Diagnosis
Complete Diagnosis Path — In Order
Follow this sequence exactly. Each step either confirms or eliminates a cause before spending money.
1
Read all codes — note which cylinder and check freeze frame
Record the exact code (P0301–P0308). Read freeze frame data — at what RPM, load, and coolant temperature did the misfire occur? Cold-start only misfires point to different causes than sustained warm idle misfires. Also note if P0300 (random misfire) is stored alongside the specific code — this is normal and doesn’t indicate a second fault.
2
Perform the coil swap test
Swap the coil from the misfiring cylinder to an adjacent cylinder. Clear codes. Drive 5–10 minutes. If the code moves — coil is bad, replace it. If the code stays — proceed to step 3. Also: while the coil is out, inspect the plug well for oil and the boot for cracks.
3
Remove and inspect the spark plug
With the suspect coil back on the original cylinder, remove the spark plug. Inspect: gap (compare to spec — find it on the emissions label under the hood), electrode condition (worn = rounded, pitted), and deposits (black carbon = rich/oil, white = lean, normal = light tan). A plug that looks significantly different from the others on the engine indicates an underlying issue on that cylinder. Replace the full set if over 60k miles.
4
Check the injector on the affected cylinder
Listen to each injector at idle with a mechanic’s stethoscope — each should click at a consistent rate. The affected cylinder’s injector should sound identical to the others. Check the injector electrical connector for corrosion. If a P020x code is stored alongside the P030x, the injector circuit has a confirmed electrical fault — check wiring and connector before replacing the injector.
5
Inspect the coil connector and wiring harness
With a known-good coil installed, inspect the connector on the affected cylinder for green corrosion, pushed-out terminals, or melted plastic. Check the harness for chafing where it passes near hot or sharp components. A voltage drop test on the coil power and ground circuits identifies wiring resistance that would prevent the coil from firing properly.
6
Compression test if all above are clear
If the coil is good (swap tested), plug is good, injector is working, and wiring is intact — do a compression test with the engine warm. The affected cylinder should read within 15% of the highest reading. A low-compression cylinder that’s misfiring despite good ignition and fuel delivery has a mechanical fault — leakdown test will identify whether the leak is at the valves, rings, or head gasket.
// 06 — Confirmed On — Vehicle-Specific Notes
Cylinder Misfire — Most Common Causes by Make
Toyota (Camry, RAV4, Tacoma)
2AZ-FE: P0304 most common — cylinder 4 coil or plug. Oil consumption in high-mileage 2AZ causes oil-fouled plugs on cylinder 4 specifically. Check plug well for oil before replacing coil. 1GR-FE V6: valve cover gasket leaks into all 6 wells — replace all coils and gasket simultaneously. Code: P0304 · P0301.
Honda (Civic, Accord, CR-V)
K-series (K20/K24): P0303 common — cylinder 3 coil failure. K24 valve cover gasket leak into cylinder 3 well is a known issue — oil destroys the coil boot. Replace valve cover gasket, clean the well, and install a new coil. B-series: plug wire failures causing cylinder-specific codes. Code: P0303 · P0302.
Ford (F-150, Explorer, Mustang)
4.6L/5.4L 3V: spark plug thread stripping — the plug blows out of the head causing P030x. This is an engine design fault on these engines. Inspect threads before blaming the coil or plug. EcoBoost 3.5L: P0301–P0304 from carbon on intake valves. Coyote 5.0L: coil failures at 80k+. Code: P0303 · P0301.
Chevy/GM (Silverado, Malibu)
3.6L V6: P0305 and P0306 most common — rear bank coils degrade fastest from heat. Known coil failure pattern at 80k. Replace all 6 coils when one fails on this engine — rear bank access is difficult and others fail shortly after. 5.3L V8: P0308 and P0307 from AFM lifter failures on rear cylinders. Code: P0305 · P0306.
BMW (3/5-Series, X3/X5)
N52/N54/N55: all cylinders susceptible — valve cover gasket and spark plug well seal failures flood all 6 plug wells with oil. Replace valve cover gasket and all 6 coils simultaneously — partial replacement leads to repeat failures within months. N20: P0301 and P0302 common from coil failure at 60–80k. Code: P0301 through P0306.
Subaru (Outback, Forester, WRX)
EJ25 boxer: P0301 and P0302 are front cylinders on the boxer — these run hotter and coils degrade faster. Heat-soak coil failure is the most common cause. EJ25 head gasket failures also cause P0301–P0304 from coolant intrusion misfires — do a block test before buying coils on any EJ25. Code: P0301 · P0302.
Still Getting the Misfire After Testing?
Tell our free AI Diagnostic tool your vehicle, the stored code, what the coil swap test showed, and the plug condition — it will give you the next specific step for your situation.
// 07 — Repair Costs
Cylinder Misfire Repairs — Cost and DIY Difficulty
| Repair | DIY Cost | Shop Cost | DIY? |
|---|---|---|---|
| Coil swap test (diagnosis) | $0 | $80–$150 diag | Yes — 10 min |
| Ignition coil replacement (single) | $30–$120 | $120–$280 | Yes — 10–15 min |
| Spark plug set (all cylinders) | $30–$120 | $150–$400 | Yes — 30–90 min |
| Coil boot replacement (per cylinder) | $5–$20 | $40–$100 | Yes — 10 min |
| Valve cover gasket (stops oil in wells) | $20–$80 gasket | $200–$600 | Moderate |
| Fuel injector cleaning (off-car) | $80–$150 | $150–$350 | Moderate |
| Fuel injector replacement (single) | $50–$200 | $150–$400 | Moderate |
| Connector pigtail repair | $5–$30 | $80–$200 | Yes — 30 min |
| Compression test (diagnosis) | $20–$30 kit | $80–$150 | Yes — DIY kit |
| Head gasket repair | Parts: $200–$600 | $1,200–$3,500 | Shop recommended |
Correct order: 1) Coil swap test ($0). 2) Inspect plug ($0 if you have a socket). 3) Replace plugs if over mileage ($30–$120). 4) Replace confirmed-bad coil ($30–$120). 5) Check injector if misfire persists after new coil and plug. 6) Compression test only if all ignition and fuel checks are clear.
// 08 — FAQs
Frequently Asked Questions
No — one problem. P0300 (random misfire) fires alongside P030x (specific cylinder) because the misfire rate on cylinder 1 has exceeded the random threshold. The PCM stores both. Fix the cylinder-specific misfire (P0301) and P0300 will clear with it after the next full drive cycle. You do not need to diagnose them as separate faults.
The coil is not the problem. In order: 1) Remove and inspect the spark plug on that cylinder — look for fouling, worn electrode, or cracked ceramic. 2) Replace the plug if it looks abnormal or is over 60k miles. 3) Check the injector — listen with a stethoscope at idle, test resistance at the connector. 4) Inspect the coil wiring connector for corrosion. 5) If all clear, do a compression test — a cylinder with low compression will misfire regardless of ignition and fuel quality.
You can, but the coil swap test is faster and free — it takes 10 minutes and zero dollars and definitively tells you whether the coil is the cause. If you replace the plug and the misfire continues, you’ve spent $10–$20 and still don’t know if the coil is bad. If you do the coil swap first and the code moves, you know exactly what to buy. If the code doesn’t move, you then know to check the plug, and that replacement will likely resolve it. The two tests take the same total time if done together.
Yes — a misfire that clears when warm points toward a coil with internal insulation that works when warm but fails when cold (less common) or, more often, a spark plug that can’t ignite the cold, dense mixture but fires fine when the mixture is warmer and easier to ignite. Cold-only misfires with a cylinder-specific code are most often resolved by plug replacement. The coil swap test still applies — do it warm if the misfire only occurs cold, and re-test cold after the swap to see if the code moved.
It depends on the engine and mileage. On most 4-cylinder engines under 100k miles — replace only the confirmed-bad coil. On 6-cylinder engines, particularly German brands (BMW, Mercedes, VW/Audi) — replace all coils simultaneously because they have the same mileage and fail in clusters. On V8s — replace the bad coil plus its immediate neighbours on the same bank if over 120k miles. On any engine where oil was in the plug wells — fix the gasket leak first, then replace all coils on the affected bank since oil exposure degrades all of them equally.
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