P0304 on Toyota vehicles Cylinder 4 is misfiring

A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.

Bulletins and campaigns Toyota filed with NHTSA whose summary names P0304. Quote the document number at the service desk — it is a diagnosis the maker has already written down.

• T-SB-0116-15 REV Service bulletin
  2016-08-11 · Hybrid Propulsion System
• TSB: REVISION NOTICE AUGUST 11, 2016 REV1: APPLICABILITY HAS BEEN UPDATED TO INCLUDE 2016 MODEL YEAR PRIUS V VEHICLES. ANY PREVIOUS PRINTED VERSIONS OF THIS BULLETIN SHOULD BE DISCARDED. SOME 2010 – 2015 MODEL YEAR PRIUS (2ZR-FXE EQUIPPED) VEHICLES, 2012 – 2015 MODEL YEAR PRIUS PHV VEHICLES, AND 2012 – 2016 PRIUS V (2ZR-FXE EQUIPPED) VEHICLES MAY EXHIBIT A “RUNS ROUGH” AND/OR MIL “ON” CONDITIO
• T-SB-0116-15 Rev Service bulletin
  2016-08-11 · Engine And Engine Cooling — Exhaust System — Emission Control — Gas Recirculation Valve (Egr Valve)
• TSB: REVISION NOTICE August 11, 2016 Rev1: Applicability has been updated to include 2016 model year Prius V vehicles. Any previous printed versions of this bulletin should be discarded. Some 2010 - 2015 model year Prius (2ZR-FXE equipped) vehicles, 2012 - 2015 model year Prius PHV vehicles, and 2012 - 2016 Prius V (2ZR-FXE equipped) vehicles may exhibit a "runs rough" and/or MIL "ON" conditio
• T-SB-0147-16 Service bulletin
  2016-10-14 · Back Over Prevention
• TSB: Some 2013 ? 2015 Prius PHV, Prius and 2013 ? 2016 Prius V vehicles may exhibit a vibration due to rough idle and/or tapping noise from the HV transaxle at cold start. The check engine light may also illuminate with (DTC) P0300, P0301, P0302, P0303, P0304 (Random/Multiple Cylinder Misfire Detected). The Engine Control Module/ECM (SAE Term: Powertrain Control Module/PCM) logic has been modifie
• T-TT-0462-17 Service bulletin
  2017-11-14 · Fuel System, Other — Storage — Tank Assembly — Pressure Relief Devices
• T-TT: Vehicles may experience various drivability concerns. Upon diagnosis, technicians commonly find no or low fuel pressure as well as a variety of DTCs (Commonly P1603, P1604, P1605, P0171, P0300, P0302, P0304, U0100). Technicians find that the cause this condition is corrosion and water in the A43 ECM connector (Fig 1). In several cases, it was found that the source of water was from aftermark
• T-SB-0072-19 Service bulletin
  2019-06-24 · Electrical System
• TSB: Some 2014 ? 2018 model year Highlander and Highlander Hybrid vehicles may exhibit one or more of the following conditions. ? Various drivability concerns ? Low or no fuel pressure ? Diagnostic Trouble Codes (DTCs) (Including but not limited to P1603, P1604, P1605, P0171, P0300, P0302, P0304, U0100) ? Some 2014 ? 2018 model year Highlander Hybrid vehicles may exhibit DTC P134A. These conditio

A stored code names the test that failed, never the part that caused it. The record above is what Toyota and its owners have filed about it; the code’s page across every make has the whole file.