P0301
Cylinder 1 Misfire Detected
If your vehicle's onboard computer has flagged the diagnostic trouble code P0301, it refers to a detected anomaly regarding "Cylinder 1 Misfire Detected". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Storing code P0301 is your car's way of telling you something is wrong with the cylinder 1 misfire detected. You may notice engine stumble, flashing mil, rough acceleration, all of which are direct consequences of this malfunction. Given the high severity of this code, continuing to drive risks significant mechanical damage. Have it diagnosed immediately.
Symptoms
Engine stumble, flashing MIL, rough acceleration
Common Causes
- Bad spark plug in cyl 1
- Faulty ignition coil
- Low compression
- Clogged fuel injector
How to Fix
- 1 Swap coil with cyl 2 to test
- 2 Replace spark plug
- 3 Perform compression test
- 4 Clean fuel injector
Technical Explanation
To set P0301, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. Misfire rate is counted per cylinder over rolling windows and compared against two thresholds: a catalyst-damaging rate (triggers flashing MIL) and an emissions-exceeding rate (triggers solid MIL). The PCM logs which cylinder is misfiring based on crankshaft position at the time of each detected event. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
An active P0301 code under high-severity conditions means the affected system is operating outside safe parameters. Continued driving — especially under load or at highway speeds — significantly increases the risk of secondary damage to components like faulty ignition coil.
Mechanic's Pro Tip
When diagnosing P0301, always test fuel volume delivery in addition to static pressure — a pump that holds pressure at idle but delivers insufficient volume under load will cause the fault only during acceleration or high demand, making it difficult to replicate in the driveway. Use a fuel pressure gauge with a volume outlet port: a healthy pump should deliver at least 1 liter per minute. Replace the fuel filter first; it's the cheapest test and solves the fault in a significant percentage of cases.
Single coil and plug: $100 - $250