P0303: Cylinder 3 Misfire Detected
The ECM detects crankshaft deceleration during Cylinder #3 combustion stroke. On Subaru boxer engines, Cylinder 3 is on the passenger side rear.
Driveability & Safety Advisory
Drive directly to repair garage. Avoid highway cruising under load.
Official Manufacturer TSB Advisories
Factory Condition: Oil consumption causes carbon buildup on Cylinder 3 exhaust valve, leading to partial valve seating failure.
Physical Component Location & Service Access
Third cylinder from front on inline engines; rear passenger side on Subaru boxer 4-cylinder engines.
Electrical Specifications & Live PID Benchmarks
Scan Tool Live Data Targets
Digital Multimeter (DMM) Specs
Documented Model-Specific Case Studies
Root Cause: Cylinder 3 plug boot carbon tracking caused by high humidity in intake air charge.
Verified Fix: Replace Cylinder 3 coil boot and spark plug.
Technician Inspection & Testing Workflow
Swap coil with Cylinder 1; check code migration.
Inspect spark plug condition.
Verify injector signal.
Cost Breakdown
Tools & Parts Matrix
Diagnostic Questions & Answers
Where is Cylinder 3 located?
On standard inline 4-cylinder engines, it is the 3rd cylinder counting from the front timing belt back toward the transmission.