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P0421 Diagnostic Trouble Code Discussion for March 2006

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2002 Audi A4 3.0L MIL Lamp on VIN: WAUYP64B51
P0421: Warm up catalyst efficiency below threshold b1. I've suspected oxygen sensors and they seem to be in range. Has anyone seen related codes for this problem?
March 07, 2006
2001 Mazda Protege ES 2.0L Cuts out, Misfire, MIL Lamp on VIN: JM1BJ22511
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). HELP!!! This car is violating all known laws of government and physics! Customer complains of "lack of power, cutting out, hot smell at rear of car--burns your nose", also the MIL comes on, FLASHES and continues to flash even with car running great. Co...
March 15, 2006