Cylinder 1 Misfire Detected
P0301 indicates a misfire detected specifically in cylinder 1: the air-fuel mixture is not igniting reliably in that cylinder. Typical causes are that cylinder's spark plug, ignition coil, or injector, or low compression. This is a high-priority fault, since unburned fuel can overheat and damage the catalytic converter, so locating and repairing the affected cylinder is the priority.
01. Most Common Causes
- The spark plug in cylinder 1 is worn or incorrectly gapped and no longer produces a spark strong enough to ignite that cylinder's mixture.
- The ignition coil (COP) on cylinder 1 is weak or cracked and delivers intermittent high voltage, causing localized misfires.
- The injector for cylinder 1 is dirty or clogged and fails to atomize fuel properly, upsetting that cylinder's air-fuel ratio.
- Low compression in cylinder 1 from burned valves, a head-gasket breach, or worn rings that prevents stable combustion.
- A localized vacuum leak or a fault in the coil or injector harness or connector for cylinder 1 that interrupts the trigger signal.
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine misfire, rough idle, or hesitation during acceleration
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Swap spark plug and ignition coil from cylinder 1 to another cylinder; if misfire moves, replace the faulty component.
Step 3: Inspect fuel injector on cylinder 1 for clogging or leakage; perform injector balance test if necessary.
Step 4: Check for vacuum leaks using smoke machine or propane enrichment near cylinder 1 intake.
Step 5: Perform compression test on cylinder 1; compare to other cylinders.
04. Tools You Will Need
- OBD2 scan tool with live per-cylinder misfire counters
- Compression tester to verify the mechanical sealing of each cylinder
- Spark tester to confirm ignition at each plug wire or coil
- Automotive oscilloscope to analyze coil and injector waveforms
- Digital multimeter to measure the primary and secondary resistance of the coils
1. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with a misfire as it can damage the catalytic converter and other engine components. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
Costs vary: a spark plug replacement is around $50-$150, ignition coil $100-$200, fuel injector $200-$400, and compression repairs can exceed $1,000.