Ignition & misfire · Powertrain · generic (SAE-defined)
P0301: Cylinder 1 Misfire Detected
P0301 means the engine computer detected that cylinder 1 is misfiring, meaning the air-fuel mixture in that cylinder is not burning properly on some combustion cycles.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0301 sets
The powertrain control module (PCM) uses the crankshaft position sensor to detect the small slowdown that happens when a cylinder does not fire. When it attributes enough of those events to cylinder 1 within a monitoring window, it sets P0301. Misfire thresholds and windows vary by manufacturer.
Common causes of P0301
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Worn or fouled spark plug in cylinder 1
- Failed ignition coil or plug wire for cylinder 1
- Clogged or leaking fuel injector for cylinder 1
- Vacuum leak near the cylinder 1 intake runner
- Low compression in cylinder 1 from a valve or ring problem
- Oil or coolant contaminating the cylinder 1 spark plug well
P0301 symptoms
- Check engine light on or flashing
- Rough idle or engine shake
- Hesitation during acceleration
- Reduced fuel economy
How P0301 is diagnosed
- Check freeze frame data and look for other misfire or fuel trim codes.
- Remove and inspect the cylinder 1 spark plug for wear, fouling, or oil.
- Swap the cylinder 1 coil with a neighboring cylinder and see if the misfire moves.
- Check the cylinder 1 injector connector and test injector operation or balance.
- Smoke-test the intake for leaks near cylinder 1.
- Perform a compression test on cylinder 1 if ignition and fuel checks pass.
Typical fixes for P0301
- Replace the spark plug (often all plugs at once)
- Replace the cylinder 1 ignition coil or plug wire
- Clean or replace the cylinder 1 fuel injector
- Repair a nearby vacuum leak or intake gasket
- Repair valve or ring damage if compression is low
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0301 FAQ
What does code P0301 mean?
P0301 means the engine computer detected that cylinder 1 is misfiring, meaning the air-fuel mixture in that cylinder is not burning properly on some combustion cycles. The standard definition is "Cylinder 1 Misfire Detected."
Can I drive with a P0301 code?
With a steady check engine light and mild roughness, a short, easy drive to a shop is usually fine. If the light flashes, stop driving soon, because unburned fuel from cylinder 1 can overheat and damage the catalytic converter.
Where is cylinder 1 on my engine?
Cylinder 1 is usually at the front of the engine, and on V engines it sits on bank 1. The exact firing order and cylinder layout should be confirmed in service information for the specific engine.
Why swap coils instead of just replacing one?
Moving the cylinder 1 coil to another cylinder shows whether the misfire follows the coil. If it does, the coil is bad; if it stays on cylinder 1, the cause is likely the plug, injector, or compression.
Keep researching
Engine guides by brand (known issues, specs)
More ignition & misfire codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.