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P0421 Diagnostic Trouble Code Discussion for September 2008

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2001 Mazda Protege ES 2.0L MIL Lamp on VIN: JM1BJ22551
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). Hello to all, this mazda intermittantly sets this po421 code. I replaced both o2s with mazda parts as the upstream was slow to switch and have over 100k on them. cleared codes road tested with passing results per [...] steps. came back again with the same cod...
September 04, 2008