P0420 on the 2002 Cadillac Deville
The bulletins listed name this code in NHTSA's summary, or are about the same components. A bulletin or a recall listed here may apply to the model year. None of it is a diagnosis.
Nobody has written a description of this code yet.
| 030604028 | 2003-08-29. Service bulletin. SERVICE ENGINE SOON (SES) LIGHT ON, REDUCED VEHICLE POWER / ACCELERATION / SPEED, DIAGNOSTIC TROUBLE CODE (DTC) P0420. *TT |
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| 090102 | 2002-04-04. Service bulletin. CONCERNS WITH DIAGNOSTIC CODES P0420, CONVERTER EFFICIENCY, P0121 TPS PERFORMANCE AND P0133 AND P0153, O2 SENSOR SLOW RESPONSE. *TT |
2 on file from NHTSA, as of 2026-10-19. See them in the bulletin list. A bulletin lists model years: read the document for which vehicles it concerns.