The ECM has detected a misfire in cylinder 1. A misfire means the air/fuel mixture in that cylinder is not igniting properly or not igniting at all.
SeverityCritical
CategoryEngine
Est. Repair Cost$50–$300
Code TypePowertrain
DIY RepairYes
DifficultyBeginner
⚡ Common Causes
›Faulty spark plug on cylinder 1
›Bad ignition coil on cylinder 1
›Clogged or failed fuel injector on cylinder 1
›Low compression in cylinder 1
⚠️ Symptoms
›Rough idle especially at startup
›Hesitation on acceleration
›Possible fuel smell from exhaust
›Check engine light on or flashing
✅ How to Fix — Step by Step
Step 1:Swap spark plug from cylinder 1 to another and recheck
Step 2:Swap ignition coil to another cylinder
Step 3:Test injector with noid light
Step 4:Perform compression test on cylinder 1
🔧 Diagnostic Tools Required
✔OBD-II Diagnostic Scanner
✔Digital Multimeter
✔Fuel Pressure Gauge
✔Compression Tester
✔Spark Tester
Using the correct diagnostic tools helps identify the root cause of P0301 before replacing parts unnecessarily. Always confirm the fault using live data and manufacturer-recommended diagnostic procedures.
🚗 Vehicles Commonly Reporting P0301
Toyota CamryHonda AccordFord FocusChevrolet CruzeNissan SentraVolkswagen Jetta
❌ Common Mistakes to Avoid
✘Replacing the cylinder 1 spark plug without first confirming it with a coil swap test
✘Assuming the coil is bad without checking for a leaking injector on that cylinder
✘Overlooking a vacuum leak specific to that intake runner
✘Not checking compression on cylinder 1 before replacing electrical parts
📋 Technical Service Bulletins
Some manufacturers publish TSBs clarifying cylinder numbering conventions (inline vs. V-configuration engines differ) — confirm which cylinder is actually "1" in your service manual before swapping parts.
🏭 Manufacturer-Specific Notes
Honda P0301
On many Honda four-cylinder engines, cylinder 1 is closest to the timing belt/chain end — check your engine's firing order diagram before swapping parts.
Ford P0301
On Ford V6 and V8 engines, cylinder 1 numbering depends on bank layout — consult the underhood emissions label for the correct cylinder map.
Volkswagen P0301
VW/Audi TSI/TFSI four-cylinder engines are known for cylinder-specific misfires from carbon-fouled direct injectors — cleaning or replacing the injector often resolves it.
🎓 Expert Tip: A misfire that stays on cylinder 1 even after swapping the spark plug and coil to another cylinder points to a mechanical issue (valve, injector, or compression) rather than an electrical one — don't keep replacing ignition parts once the swap test rules them out.
💡 Pro Tip: Always swap parts to another cylinder to confirm the fault follows the part.
Repair Cost Estimate
Full Repair Estimate
$50–$300
DIY Possible?
YES
Severity
Critical
Diagnosis Time
20–40 minutes
Repair Time
30–90 minutes
Frequently Asked Questions
What does OBD2 code P0301 mean?+
P0301 stands for Cylinder 1 Misfire Detected. The ECM has detected a misfire in cylinder 1. A misfire means the air/fuel mixture in that cylinder is not igniting properly or not igniting at all.
What causes code P0301?+
Faulty spark plug on cylinder 1; Bad ignition coil on cylinder 1; Clogged or failed fuel injector on cylinder 1; Low compression in cylinder 1
How do I fix code P0301?+
Swap spark plug from cylinder 1 to another and recheck; Swap ignition coil to another cylinder; Test injector with noid light; Perform compression test on cylinder 1
How much does it cost to fix P0301?+
Estimated repair cost for P0301 is $50–$300.
Is P0301 DIY-friendly?+
Yes — P0301 is generally DIY-friendly with basic tools.
References
SAE J1979 — E/E Diagnostic Test Modes (OBD-II communication standard)
ISO 15031 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics
Vehicle manufacturer service manual (consult your specific make and model)
