Engine Misfire P0300-P0304: How to Test an Ignition Coil (Toyota / Nissan / Jeep)
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Why P0300–P0304 appears on coil-on-plug engines
On any engine built in the last two decades, ignition is coil-on-plug: every cylinder carries its own ignition coil sitting directly on top of its spark plug, and the engine computer fires each one individually. That design is good news for diagnosis, because the computer can count misfires per cylinder and tell you exactly where the problem is.
The code you are reading does not say "your coil is dead." It says the crankshaft slowed down more than expected on a specific cylinder, in a specific window. That can come from four places:
- The ignition coil — insulation breaks down with heat cycles, the internal winding shorts, or the boot cracks and arcs to the cylinder head. This is the most common cause and the easiest to confirm.
- The spark plug — electrode gap grows with mileage, so the voltage needed to fire rises until, under load, the coil can no longer jump it. A plug that looks "fine" at idle can misfire at 2,500 rpm.
- Fuel delivery — a clogged or leaking injector leans out one cylinder. A P0301 with a plug that looks bone white is a fuel clue, not an ignition clue.
- Mechanical — low compression from valves, rings or a head gasket. A misfire that survives a new coil and a new plug is mechanical until proven otherwise.
Do not throw a full set of coils at a P0301 before you have moved one coil to a different cylinder. The swap test below takes fifteen minutes and is the single step that separates a $50 fix from a $500 guess.
Symptoms and fault codes: what points where
| Symptom | What it usually means |
|---|---|
| Rough idle, noticeable shake at traffic lights, smooths out above ~1,500 rpm | One cylinder dropping out — classic single-cylinder coil or plug fault |
| Hesitation or stumble under load, worse on hills or with the A/C on | Voltage demand at high cylinder pressure exceeds what a weak coil can deliver |
| Misfire only when cold, clears when warm | Moisture or a hairline crack in the coil boot arcing across a cold, damp insulator |
| Misfire only when hot, appears after 20+ minutes of driving | Heat-soaked coil winding breaking down internally — the failure most often missed by a cold-engine test |
| Pulsing or flashing check engine light while driving | An active misfire dumping unburned fuel into the catalytic converter — stop driving |
| Misfire plus a rotten-egg smell or a P0420 shortly after | The converter is already being damaged by the raw fuel |
| Oil around the top of the spark plug or on the coil boot | Failed valve cover / spark plug tube seal feeding an ignition fault — fix the leak or it will kill the new coil |
| Code | Meaning | First move |
|---|---|---|
| P0300 | Random / multiple cylinder misfire | Look for a shared cause: fuel pressure, vacuum leak, or a whole-set ignition service that is overdue |
| P0301 – P0304 | Misfire on cylinder 1, 2, 3 or 4 (P0305–P0306 continue on V6 engines) | Treat as a single-cylinder fault: swap test that coil first |
| P0300 + P0301–P0306 together | Misfire on more than one cylinder | Check the common cause — fuel, vacuum, or ignition parts well past their service life |
| P0351 – P0356 | Ignition coil primary/secondary circuit fault for that cylinder | Reads as an electrical fault: check the connector, wiring and coil, not the plug alone |
| P030x + P0171 / P0174 | Misfire alongside lean-bank codes | A vacuum or intake leak that is leaning out one bank — diagnose that before buying ignition parts |
| P030x + P0420 | Misfire that has already affected the converter | Fix ignition first, then re-check: converters sometimes recover once the misfire stops |
Codes above are the generic OBD-II definitions reported by any scan tool. Always read the freeze-frame data — the rpm, load and coolant temperature when the code set — before deciding what to replace.
How to test a coil-on-plug ignition coil in the driveway
- Read the codes and write down the cylinder number. Scan the live misfire counters too if your tool supports them; a cylinder counting thousands of misfires while the others count zero is the one to chase. Clear the codes only after recording them.
- Inspect before you test. Lift the coil for the flagged cylinder and look at the boot. A carbon track, a white powder ring, a crack, or an oily film on the rubber means the coil has been arcing to ground rather than firing the plug. Check the connector for corrosion or a broken retaining clip at the same time.
- Look at the spark plug while the coil is out. The plug is a free diagnostic report: oil-fouled points at a tube seal, black dry soot at a rich condition, glazed white at a lean condition, and eroded electrodes mean the gap has opened with mileage.
- Run the swap test — the decisive step. Move the suspect coil to a different cylinder and reinstall a known-good coil into the flagged cylinder. Clear the codes and drive the same conditions as before, then re-read. Misfire follows the coil = replace the coil. Misfire stays on the original cylinder = the coil is innocent; move to the plug, the injector, then compression.
- Decide between fixing and replacing the set. If one coil has failed at 100,000+ miles, the identical coils around it have lived the same number of heat cycles. On a transverse V6 where the rear bank hides under the intake plenum, replacing all six at once is cheaper than paying the same teardown labour twice.
- Install with the right practice. A thin smear of dielectric grease inside the boot, plugs threaded in by hand before any wrench is applied, and a careful check that the coil connector clicks fully home. Loose or cross-threaded plugs cause the next misfire.
- Clear the codes and confirm with a drive cycle. After clearing, run an mixed cycle — idle, steady cruise, and a couple of loaded pulls. Readiness monitors may need several trips before the light stays off. If the misfire returns immediately on the same cylinder with new ignition parts, stop and test compression.
On torque values: tightening specifications for spark plugs and coil retaining fasteners differ by engine family and by plug thread size. VeloCore does not publish torque numbers here — use the value in your vehicle's factory service information, and use a torque wrench in the range the spec calls for. Over-tightening a plug in an aluminium head is a repair that costs far more than the plug.
Coil and plug kits for Toyota, Nissan, Jeep and Chrysler
Every kit below is supplied as coils plus the matching spark plugs, because on a coil-on-plug engine the two wear together and mixing a new coil with a 90,000-mile plug is how a fresh coil gets blamed for an old problem.
| Vehicle | Engine | OE / reference number | Part |
|---|---|---|---|
| Toyota 4Runner 2013–2024, FJ Cruiser 2014, Tundra 2013–2014 Also listed L4: Camry 2010–2017 2.5L, RAV4 2009–2018 2.5L, Highlander 2009–2019 2.7L, Sienna 2011–2013 2.7L, Venza 2009–2016 2.7L, Scion tC 2011–2016 2.5L — these use 4 coils and 4 plugs, keep 2 as spares |
4.0L V6 (6+6 kit) L4: 2.5L / 2.7L |
90919-A2005 / UF487 Also: 90919-A2003, 90919-02250, 90919-02255/02256 — plugs 5018 / LFR5AGP |
VeloCore Ignition Coil & Plug Kit 90919-A2005, 6 UF487 coils + 6 platinum plugs — $70.15 |
| Nissan Altima 2007–2012 2.5L (incl. 2013 Altima Coupe 2.5L), Rogue 2008–2013 2.5L, Rogue Select 2014–2015, Sentra 2007–2012 2.0L, Sentra SE-R 2007–2012 2.5L, Cube 2009–2014 1.8L, Versa 2007–2011 1.8L | 1.8L / 2.0L / 2.5L L4 Not for Altima 3.5L, 2014–2015 new-generation Rogue, or Sentra 1.6L Turbo |
22448-ED000 / UF549 | VeloCore Ignition Coil Set UF549, 4 coils + 4 platinum plugs — $41.55 |
| Nissan Murano 2009–2020, Pathfinder 2013–2020, Quest 2011–2017, Altima V6 2007–2018 (coupe & sedan), Maxima 2009–2014 / 2016–2020 Infiniti QX60 2014–2020, FX35 2009–2012, Q50 2014–2018 |
3.5L V6 (VQ series) only — 6 coils + 6 iridium plugs The rear bank sits under the intake plenum: do the whole set in one teardown |
22448-JA10C / UF550 (C1670) Also: 22448-JA10A, 22448-JA11C, 22448-1KT1A |
VeloCore UF550 Coil & Iridium Plug Set, 6 + 6 — $62.85 |
| Toyota Corolla 2009–2018 1.8L and 2019 Sedan 1.8L, Corolla iM 2017–2018, Matrix 2009–2013, Prius 2010–2015, Prius Plug-in 2012–2015, Prius v 2012–2017, C-HR 2018–2021 2.0L Lexus CT200h 2011–2017, Scion iM 2016, Scion xD 2008–2014 |
1.8L L4 (plus C-HR 2.0L) 4 coils + 4 iridium plugs |
90919-02252 / UF596 Also: UF619, 90919-02258 — plugs 90919-01275 / Denso SC16HR11 |
VeloCore Ignition Coil Set UF596, 4 coils + 4 iridium plugs — $41.99 |
| Chrysler 200 2011–2017, 300 2011–2020, Town & Country 2011–2016 Dodge Avenger 2011–2014, Challenger / Charger 2011–2020, Durango 2011–2015, Grand Caravan 2011–2020, Journey 2011–2019 Jeep Wrangler 2012–2017 and Wrangler JK 2018 3.6L, Grand Cherokee 2011–2015 3.6L, Cherokee 2014–2020 3.2L Ram 1500 2013–2018, 1500 Classic 2019–2020, C/V 2012–2015, ProMaster 1500/2500/3500 2014–2020 VW Routan 2011–2014 |
3.6L V6 (and 3.2L V6) 2-pin coil connector — 6 coils + 6 laser iridium plugs |
5149168AH / UF648 Also: 5149168AI/AJ, C1791, 5C1848, E1148, GN10616, 0221504032 — plugs 9723 / SILZKR7B11 |
VeloCore Ignition Coil & Plug Kit 5149168AH, 6 UF648 coils + 6 laser iridium plugs — $49.99 |
See every VeloCore ignition and engine part →
FAQ
Can I keep driving with a P0301 misfire?
Only far enough to stop safely. An active misfire sends unburned fuel into the catalytic converter, where it burns and overheats the substrate. A converter replacement costs many times more than the coil causing the code. If the check engine light is flashing, the misfire is active right now and driving should stop immediately.
How do I tell whether it is the coil or the spark plug?
Use the swap test. Move the suspect coil to another cylinder and a known-good coil into the flagged one, clear the codes and repeat the same driving conditions. If the misfire code follows the coil, the coil is the fault. If the code stays on the original cylinder, test the plug, the injector and compression. Because coils and plugs wear on the same duty cycle, replacing both together is the standard practice on coil-on-plug engines.
Do I need to replace all the coils, or just the bad one?
One coil will get the car running. But coils on the same engine share the same age, the same heat cycles and the same duty, so a second failure is common within months. On engines where the rear bank is buried under the intake plenum — the Nissan 3.5L V6 in the Murano, Quest and Altima V6, for example — replacing all six in one teardown costs far less than paying that labour twice.
Why does my misfire only happen when the engine is hot or under load?
Both conditions raise the voltage needed to fire the plug. A coil with a hairline insulation crack or a partially shorted winding can still fire a plug at idle in a cold engine, then break down once heat and cylinder pressure increase. That is why a cold-engine bench inspection passes and the driver's complaint is real — always reproduce the fault under the conditions that trigger it.
Is the UF number alone enough to order the right coil?
No. A coil reference number identifies one component, not a complete application — the same UF549 coil number can be used with more than one spark plug depending on year and engine. Always confirm the year, model, engine size and the part numbers stamped on the components you are removing. Our fitment tables list the engine sizes each kit is built for; if your engine is not listed, send us your VIN before ordering.
Not sure which kit fits? Send us your VIN and the number stamped on your original coil and we will confirm the correct coil-and-plug set for your engine before you order. Every VeloCore ignition part is covered by our Fitment Guarantee — it fits, or we make it right.
Related reading
More diagnostic guides from the VeloCore workshop:
- Throttle Body Failure: P0121/P2135 Symptoms and Replacement Guide — the misfire could actually be an airflow fault
- Water Pump Failure: Diagnosing Coolant Leaks & Overheating — coolant loss that is mimicking a misfire
- Power steering pump failure: whining noise & hard steering
- How to test a bad alternator (P2503/P0620)
- Fuel injector symptoms: clean vs replace (P0201)