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P0421 Diagnostic Trouble Code Discussion for February 2010

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2001 Mazda Millenia 2.5L MIL Lamp on VIN: JM1TA22141
P0421: Catalyst Efficiency Below Normal (Bank 1). ... among other things it fails emission for 2 codes in computer. p0421 and p0431 catalyst efficiency below threshold bank 1 and 2. plugged scanner in and found upstream and downstream were doing the same switching on both banks which tells me that the cats ar...
February 08, 2010
2002 Mitsubishi Lancer ES 2.0L MIL Lamp on VIN: JA3AJ26E12
P0421: Warmup Catalyst Efficiency Low (Bank 1). ... cat does a melt down at end of cat,and needs new oem, and flash. With the feed to O2 heater,I have 12 volts,but I can't light a test light,red and blue wire,from mfi relay and pcm.If I have a O2 heater problem,that would cause the P0421 ,right,and I would ...
February 12, 2010