P0420 on Hyundai vehicles The catalytic converter on bank 1 is not cleaning up the exhaust as well as it should

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.

Owners’ own words, scrubbed of anything identifying. Unverified reports filed with NHTSA — what was said, not a finding that it was true.

Bulletins and campaigns Hyundai filed with NHTSA whose summary names P0420. Quote the document number at the service desk — it is a diagnosis the maker has already written down.

• 20-FL-010H Service bulletin
  2020-10-19 · Engine And Engine Cooling
• This bulletin provides information related to the repair of DTC P0420 “Catalytic Converter System Bank 1 - Efficiency Below Threshold” found stored in the Engine Control Module (ECM). The repair involves performing an ECM Update and replacement of the exhaust manifold catalyst.
• 5NP-F8N6C-10 Service bulletin
  2016-09-23 · Electrical System — Software
• "THIS BULLETIN PROVIDES INFORMATION RELATED TO THE ENGINE CONTROL MODULE (ECM) SOFTWARE UPDATE TO PREVENT AN INCREASE IN THE CATALYST TEMPERATURE WHICH MAY RESULT IN ILLUMINATION OF THE MALFUNCTION INDICATOR LIGHT WITH THE FOLLOWING DTC(S): „H P0171 - SYSTEM TOO LEAN - BANK 1. „H P0420 - CATALYTIC CONVERTER SYSTEM, BANK 1 - EFFICIENCY BELOW THRESHOLD. IN RARE CASES, THERE CAN BE A REDUCTION IN

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