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Home › Mazda › 2003 › MPV ES › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P0421 Or DTC P0431 › Possible Causes

Possible Causes

Exhaust system leaks.
Front HO2S malfunction.
Loose front or rear HO2S.
Warm Up Three Way Catalytic (WU-TWC) converter deterioration or malfunction.