P0301 Code: Cylinder 1 Misfire Detected
Cylinder 1 is repeatedly failing to fire. The cause is almost always its coil, plug, injector or compression.
At a glance
Severity: Moderate
- Meaning
- Cylinder 1 Misfire Detected
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $90–$3,500
- DIY difficulty
- Easy
The engine computer watches crankshaft speed, and each time cylinder 1 should be on its power stroke it expects a small push. P0301 means that push has gone missing often enough to raise emissions. Because only one cylinder is affected, the fault is almost always something local to it: its coil, spark plug, injector, intake seal or compression. Cylinder 1 sits at the timing-belt or chain end of an inline engine and at the front of bank 1 on a V engine, but where that is under the hood varies by manufacturer. So confirm the numbering for your engine before you buy parts.
Can I keep driving? You can usually drive a short distance to a shop with a steady light, but keep it gentle: no towing, no full throttle. If the light starts flashing, stop driving, because the unburned fuel from cylinder 1 is overheating the catalytic converter.
How to read P0301
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 01 Specific fault
Symptoms
- Steady rhythmic shake at idle, like one beat missing in every engine cycle
- Check-engine light on, flashing during harder acceleration
- Stumble or jerk when accelerating from a stop
- Slight loss of power and lower gas mileage
- Exhaust puffs unevenly at the tailpipe at idle
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Worn, cracked or oil-soaked spark plug in cylinder 1, often from a leaking plug tube seal
- Failing ignition coil or cracked coil boot on cylinder 1
- Clogged or leaking fuel injector for cylinder 1
- Low compression in cylinder 1 (burned exhaust valve, tight valve clearance or worn rings)
- Vacuum leak at the cylinder 1 intake runner or its gasket
- Damaged wiring or a loose connector at the cylinder 1 coil or injector
Diagnosis step by step
Find out where cylinder 1 really is
Check the cylinder layout for your exact engine. On GM small-block V8s cylinder 1 is at the front of the driver's side, and on Ford 4.6/5.4 V8s it is at the front of the passenger side. On many transverse V6s, including Honda's 3.5L and Toyota's 3.5L, it is on the rear bank against the firewall, so plan extra time: the intake plenum or cowl usually has to come off.
Tools: Flashlight
Swap the cylinder 1 coil with a neighbor
With the engine off, swap the cylinder 1 coil with an easy-to-reach neighbor, clear the code and drive the same way that set it. If the misfire follows the coil (for example, it becomes P0302), you have found a bad coil. If it stays on cylinder 1, the coil is fine.
Tools: Screwdriver, OBD-II scanner
Pull and read the cylinder 1 plug
Let the engine cool before you remove the plug. Look for a cracked insulator, carbon tracking on the porcelain, oil on the threads, or a gap far larger than the others. Oil pooled in the plug well means a leaking tube seal or valve cover gasket, and that oil will keep destroying coil boots until it is fixed.
Tools: Spark plug socket, Flashlight
Check injector 1
With the engine idling, hold a mechanic's stethoscope or a long screwdriver on the injector and listen for a crisp, even clicking. Then compare its resistance with the other injectors using a multimeter. An injector that is silent, or that reads well outside the others, needs further testing or replacement.
Tools: Multimeter, Screwdriver
Compression test on cylinder 1
If coil, plug and injector are fine, measure compression on cylinder 1 and at least one other cylinder. If it is low, squirt a teaspoon of oil into the cylinder and retest. A big rise points to rings, and no change points to a valve or the head gasket.
Tools: Compression tester
Smoke-test the runner 1 area
A leaking intake gasket at one runner leans out only that cylinder, mostly at idle. Smoke-test the intake and watch closely around runner 1 and any vacuum fittings nearby.
Tools: Smoke machine
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace cylinder 1 ignition coil | Yes | $90–$300 |
| Replace spark plugs (full set recommended) | Yes | $120–$450 |
| Replace valve cover gasket and plug tube seals (oil in plug well) | No | $180–$500 |
| Replace cylinder 1 fuel injector | No | $200–$600 |
| Cylinder head or valve repair for low compression | No | $1,500–$3,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
The 5.4L three-valve V8 (F-150, Expedition) uses a two-piece spark plug design that is well known for breaking off in the head during removal. If cylinder 1 needs a new plug, follow Ford's removal procedure or have a shop with the extraction tool do it.
Field data
| Ford | 127 | ||
|---|---|---|---|
| Honda | 78 | Odyssey, Cr-V, Accord | |
| Hyundai | 16 | ||
| Kia | 12 | ||
| Chevrolet | 11 | Cruze, Malibu Eco, Equinox | |
| Toyota | 5 | Corolla, Highlander, Highlander Hybrid | |
| Jeep | 4 | Wrangler Unlimited, Grand Cherokee Srt, Wrangler | |
| Chrysler | 3 | Pacifica, Town And Country |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
Any stored misfire code with the check-engine light on fails an OBD smog check. The misfire monitor re-checks itself quickly after a repair, but clearing codes resets the other monitors too, so allow a few days of mixed driving before testing.
Frequently asked questions
Which cylinder is number 1 on my engine?
It is always at the timing-drive end of bank 1, but manufacturers number their cylinders differently. GM and Toyota alternate cylinders between the two banks, while Ford and Honda number one bank first. Your repair manual, or a cylinder diagram for your exact engine code, settles it.
I swapped the coil and the misfire stayed on cylinder 1. What next?
That clears the coil. Swap or replace the plug next, then test the injector, then run a compression test. Only look at the computer or its wiring once all four of those check out.
Why do I have both P0301 and P0300?
The computer sets P0300 when it sees misfires it cannot pin to a single cylinder, and a strong cylinder 1 misfire can briefly spill over into neighboring counts. Fix cylinder 1 first, clear the codes and see whether P0300 comes back on its own.
Can I replace just the cylinder 1 plug?
You can, but if the other plugs are the same age they are close behind. On engines where cylinder 1 is behind the intake plenum, it makes sense to replace the full set while everything is apart.