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P0421 Diagnostic Trouble Code Discussion for November 2007

Warmup Catalyst Efficiency Low (Bank 1)


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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2001 Mitsubishi Montero Sport ES 3.0L MIL Lamp on VIN: JA4LS2AH61
P0421: Warmup Catalyst Efficiency Low (Bank 1). owner has been driving with the mil light on since 2003, and has replaced cat converter in 04 and pcm in 03. we replaced rear o2 sensor in 04. sensors appear to be operating normally, rich/lean on the front and relatively "flat-line" on the rear o2 sen...
November 01, 2007