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P0421 Diagnostic Trouble Code Discussion for June 2011

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2002 Mazda Protege DX 2.0L MIL Lamp on VIN: JM1BJ52251
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). ... idle. Check engine light came on with P0421. Looked at O2 sensors, front one switched at about .5 of a cycle per second. I thought this was very lazy. Put in a new sensor, and it switches not much faster - about 1 time per second. So, this switch rate seem...
June 01, 2011