P1399 — Random Cylinder Misfire Detected
CAUTIONIs it safe to drive? Drive gently and get it looked at soon — it can worsen or fail inspection.
What P1399 means
This is a manufacturer-specific code — its meaning depends on the vehicle’s make (see below).
What P1399 means on specific makes
Honda / Acura CAUTION
Honda's manufacturer-specific random-misfire code (analogous to generic P0300). The PCM sees misfires across multiple/varying cylinders. Common roots are ignition, fuel, or compression/valve issues.
- Worn spark plugs / ignition coils ($40-200)
- Vacuum or intake leak
- Fuel delivery (injectors, pressure)
- Valve adjustment / mechanical (head gasket on some)
Check first: Pull freeze-frame, check plugs/coils and fuel trims; on high-mileage Hondas also verify valve clearance. Severe misfire can damage the catalyst — go easy until fixed.
Source: carparts.com/blog/p1399-code-random-cylinder-misfire-detected