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P0421 Diagnostic Trouble Code Discussion for July 2009

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
1998 Mazda Protege DX 1.5L Poor Idle Quality, Surge, MIL Lamp on VIN: JM1BC1414W
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). ... 0170 ,p 0300 ,p 0421, p1170 faults recorded check for intake leaks and for ignition leaks none found plugs look good new customer could use alittle help thanks
July 22, 2009
2001 Hyundai Santa Fe GL 2.4L Cuts out VIN: KM8SB82B91
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). Hi Techs, I'm pulling my hair out on this one. After a through warm up, at slow speeds the engine will start fluttering and will die out at a stop, it will restart easy. It did it for me twice in three days and I had the Modis on it the 2d time. The Modis show...
July 31, 2009