× Auto Repair Pros Member Benefits TechHelp Knowledge Base Forums Resources My iATN Marketplace Chat Pricing About Us Join Industry Sponsors Video Members Only Repair Shops Auto Pro Careers Auto Pro Reviews
Join Now
International Automotive Technicians Network

P0421 Diagnostic Trouble Code Discussion for November 2008

Warmup Catalyst Efficiency Low (Bank 1)

Note: This is a professional automotive technician's resource.
Vehicle Owners: If you are seeking an automotive repair professional to service your vehicle, visit the iATN Repair Shop Finder.

Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2003 Mazda Protege ES 2.0L Misfire, MIL Lamp on VIN: JM1BJ22583
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). had po3oob code , replaced plugs and filters then it has come back with multiple missfire code and cat. efficency below thresshold .../. what does this mean . is it related to the front or rear o2 sensor , and the multiple missfire code ?? any help appreciated
November 04, 2008
2003 Mazda MPV LS 3.0L MIL Lamp on, P0421 VIN: JM3LW28A53
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). P0421 sets just after other shop performed above work!!..perhaps ect??no code for it eng temp ok..data stream o.k.
November 22, 2008