P0301 Code: Cylinder 1 Misfire Detected
The P0301 trouble code means the engine computer detected a misfire in cylinder 1. A cylinder-specific misfire is usually caused by ignition problems (spark plug/coil), fuel delivery issues (injector), vacuum leaks affecting that cylinder, or mechanical problems like low compression.
What Does P0301 Mean?
A misfire means cylinder 1 isn’t producing consistent power. The PCM detects this by monitoring crankshaft speed changes. The root cause is typically something that prevents proper combustion: not enough spark, not enough fuel, too much/too little air, or a mechanical issue that reduces compression.
Symptoms of P0301
- Rough idle or shaking at idle
- Hesitation or stumble during acceleration
- Loss of power / poor acceleration
- Hard starting
- Fuel smell from exhaust (sometimes)
- Check Engine Light on (may flash if severe)
Common Causes of P0301
Ignition (Most Common)
- Worn or fouled spark plug on cylinder 1
- Weak or failing ignition coil (coil-on-plug or coil pack)
- Damaged plug wire (if equipped)
- Oil or moisture in the plug well
Fuel Delivery
- Clogged or failing fuel injector on cylinder 1
- Injector wiring/connector issues
- Low fuel pressure (can still set a cylinder-specific code)
Air / Vacuum Leaks
- Vacuum leak near cylinder 1 intake runner
- Intake manifold gasket leak
- PCV system leaks
Mechanical
- Low compression on cylinder 1
- Burnt/sticking valve
- Timing issues
- Head gasket problems (less common, but possible)
How Serious Is P0301?
A minor, intermittent misfire may feel small at first, but it can worsen quickly. Continuous misfires can overheat the catalytic converter and create expensive emissions repairs. If drivability is poor or the CEL flashes, the issue should be addressed promptly.
How to Diagnose P0301
- Check for additional codes (lean codes, fuel trim codes, other misfire codes).
- Inspect cylinder 1 spark plug for wear, cracks, oil fouling, or incorrect gap.
- Inspect ignition coil and boot for cracks, carbon tracking, or oil contamination.
- Check injector operation for cylinder 1 (consistent clicking and secure connector).
- Review fuel trims to see if a lean condition is contributing to the misfire.
- Inspect for vacuum leaks near the intake manifold and hoses.
- Compression test if ignition and fuel checks don’t resolve the misfire.
How to Fix P0301 (Most Effective Repairs)
| Repair | Most likely when |
|---|---|
| Replace spark plug (cyl 1) | Plug is worn, fouled, cracked, or gap is incorrect |
| Replace ignition coil (cyl 1) | Coil shows failure signs or spark strength is inconsistent |
| Repair oil/moisture intrusion | Oil in plug well or water intrusion causing intermittent misfire |
| Service/replace fuel injector (cyl 1) | Injector restricted/failing or connector/wiring is faulty |
| Repair vacuum leak / intake gasket | Lean trims or hissing/leak symptoms near intake |
| Mechanical repair | Compression is low or valve/timing issues are present |
P0301 Repair Cost Estimates
| Repair | Estimated Cost |
|---|---|
| Spark plug replacement | $30 – $150 |
| Ignition coil replacement | $80 – $350 |
| Fuel injector cleaning | $80 – $200 |
| Fuel injector replacement | $150 – $600 |
| Vacuum leak repair | $50 – $250 |
| Compression/leak-down testing | $120 – $300 |
FAQs
Can I drive with a P0301 code?
If symptoms are mild, short trips may be possible, but driving with a misfire can damage the catalytic converter. If the CEL is flashing or the engine is shaking heavily, driving should be avoided.
What causes cylinder 1 misfire most often?
The most common causes are a worn spark plug, failing coil, or fuel injector issue. Vacuum leaks near the intake can also contribute.
How is P0301 different from P0300?
P0301 points to cylinder 1 specifically. P0300 indicates random or multiple cylinder misfires.