Summary
P0301 means the PCM detected repeated misfires specifically in cylinder 1. The most common causes are a worn spark plug (35%), a failing ignition coil (30%), and a faulty fuel injector (15%). Unlike P0300 (random misfire), a single-cylinder code narrows the problem to components serving cylinder 1 only. Start by swapping the cylinder 1 ignition coil with an adjacent cylinder — if the misfire moves, the coil is the problem ($20–$80 part).
Severity: Moderate to High — misfires damage catalytic converters
Safe to drive: Not recommended — catalyst damage from unburned fuel
Repair cost: $20–$500 depending on cause
DIY difficulty: Easy to Moderate
What does P0301 mean?
The PCM monitors crankshaft acceleration to detect misfires. Each time a cylinder fires, the crankshaft speeds up slightly. When cylinder 1 fails to fire, there's a detectable dip in crankshaft speed at the position in the firing order where cylinder 1 should have contributed. P0301 sets when the misfire count for cylinder 1 exceeds the PCM's threshold over a monitored window.
A single-cylinder misfire code is actually good news for diagnosis — it tells you exactly where to look. The problem is almost always in the ignition, fuel delivery, or mechanical condition of that specific cylinder.
If P0300 (random misfire) is also present alongside P0301, the cylinder 1 misfire may be the worst but not the only issue. Check the other cylinders too.