A misfire has been detected in cylinder 2. Repeated misfires can damage the catalytic converter and oxygen sensors.
SeverityCritical
CategoryEngine
Est. Repair Cost$50–$350
Code TypePowertrain
DIY RepairYes
DifficultyBeginner
⚡ Common Causes
›Worn spark plug cylinder 2
›Failed coil-on-plug cylinder 2
›Injector failure on cylinder 2
›Burnt valve or low compression
⚠️ Symptoms
›Rough idle
›Check engine light on
›Reduced power and acceleration
›Possible raw fuel smell
✅ How to Fix — Step by Step
Step 1:Replace spark plug cylinder 2
Step 2:Replace ignition coil
Step 3:Test or replace fuel injector
Step 4:Perform leak-down test on cylinder 2
🔧 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 P0302 before replacing parts unnecessarily. Always confirm the fault using live data and manufacturer-recommended diagnostic procedures.
🚗 Vehicles Commonly Reporting P0302
Toyota CorollaHonda CivicFord EscapeChevrolet MalibuNissan AltimaMazda3
❌ Common Mistakes to Avoid
✘Replacing the coil before checking for oil contamination in the plug well
✘Skipping a leak-down test when a burnt valve is suspected
✘Not verifying the injector is actually firing before replacing it
✘Ignoring a recurring oil leak that keeps re-fouling the coil boot
📋 Technical Service Bulletins
Oil-fouled coil boots from a leaking valve cover gasket are a common documented cause on several engine families — check for a valve cover gasket TSB before assuming the coil itself has failed.
🏭 Manufacturer-Specific Notes
Toyota P0302
Valve cover gasket leaks that foul the spark plug tube are a frequent cause of a single-cylinder misfire on higher-mileage four-cylinder Toyota engines.
Mazda P0302
Skyactiv engines can set this code from carbon buildup on the intake valve for that cylinder — a walnut-blast cleaning is a common fix on direct-injection versions.
Chevrolet P0302
GM Ecotec engines are prone to ignition coil boot cracking, which lets oil or moisture reach the plug — inspect the boot itself, not just the coil.
🎓 Expert Tip: If the plug well is wet with oil when you pull the coil, replacing the coil alone won't fix it for long — the valve cover gasket needs to be addressed or the new coil will fail the same way.
💡 Pro Tip: Check for oil on the spark plug tip — it indicates a leaking valve cover gasket affecting the coil.
Repair Cost Estimate
Full Repair Estimate
$50–$350
DIY Possible?
YES
Severity
Critical
Diagnosis Time
20–40 minutes
Repair Time
30 minutes–2 hours (longer if a valve cover gasket needs replacing too)
Frequently Asked Questions
What does OBD2 code P0302 mean?+
P0302 stands for Cylinder 2 Misfire Detected. A misfire has been detected in cylinder 2. Repeated misfires can damage the catalytic converter and oxygen sensors.
What causes code P0302?+
Worn spark plug cylinder 2; Failed coil-on-plug cylinder 2; Injector failure on cylinder 2; Burnt valve or low compression
How do I fix code P0302?+
Replace spark plug cylinder 2; Replace ignition coil; Test or replace fuel injector; Perform leak-down test on cylinder 2
How much does it cost to fix P0302?+
Estimated repair cost for P0302 is $50–$350.
Is P0302 DIY-friendly?+
Yes — P0302 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)
