If your 2023 Toyota Prius is displaying a P0305 code indicating a cylinder 5 misfire, this code requires diagnostic investigation. The 2023 Prius represents a complete redesign featuring a new 2.0-liter four-cylinder engine (M20A-FXS). Since this engine has only four cylinders numbered 1 through 4, a code referencing cylinder 5 is technically impossible and indicates an anomalous condition requiring investigation.
The New Fifth-Generation Prius
The 2023 Prius is a ground-up redesign built on Toyota's TNGA-C platform. It uses a new 2.0-liter Atkinson-cycle four-cylinder engine paired with electric motors for significantly improved performance over the previous generation—producing 194 to 220 horsepower depending on trim. Despite the larger, more powerful engine, it remains a four-cylinder configuration without a cylinder 5.
Why P0305 May Appear on a Four-Cylinder Engine
On first-year production vehicles like the redesigned 2023 Prius, ECM software calibration issues can occasionally produce erroneous codes. Diagnostic equipment compatibility with new vehicle platforms may also cause misread codes. Communication errors between aftermarket scan tools and the new Prius electronics are possible. Finally, low 12-volt auxiliary battery voltage can cause unpredictable code storage in hybrid vehicles.
Recommended Diagnostic Approach
Use a late-model compatible scan tool to verify the stored codes and review freeze frame data. Check for any Technical Service Bulletins (TSBs) related to the 2023 Prius ECM software. If actual misfire symptoms exist, investigate cylinders 1-4 using standard misfire diagnostic procedures. Check the 12-volt battery condition, and verify all ground connections are secure.
New Platform Considerations
The 2023 Prius uses extensive new technology including a lithium-ion battery pack and redesigned power electronics. Early production units may have software updates available to address various calibration refinements.