DTC P0421 Or DTC P0431: Notes

WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Right front HO2S is identified as O2S11. Right rear HO2S is identified as O2S12. Left front HO2S is identified as O2S21. Left rear HO2S is identified as O2S22.

Code Definition

DTC P0421: Right Side Warm-Up Catalyst System Efficiency Below Threshold
DTC P0431: Left Side Warm-Up Catalyst System Efficiency Below Threshold