[Donki]

The engine check light came on 3 days after I pulled a 2009 Mazda 3 hatchback from the dealership. Brought it to Autozone for a quick check and got code P0421 Warm-up Catalyst Efficiency Below Normal (Bank 1).

Before I decide to spend $700-$1000 for repairs or replacement, I decided to post on here to see if there's anything I could do or look at myself before spending money. I'm still making payments on it so I don't want to spend needlessly when it's something I can do myself. I went on YouTube and it mostly came up with O2 sensors, but it seems like this is just trying the system into thinking it's fine (or legitimately could be bad O2 sensors.) I saw another where a guy poured lacquer thinner into the gas tank at half empty and I looked this up. People claim this worked, but it's mostly on older cars. I'm not willing to pour lacquer thinner into a '09 car I just bought.

Any suggestions?

 

[sparkybuoy]

this is caused by a STICKING THERMOSTAT causing the engine not to warm up fast enough

 

[MrBen]

The engine check light came on 3 days after I pulled a 2009 Mazda 3 hatchback from the dealership. Brought it to Autozone for a quick check and got code P0421 Warm-up Catalyst Efficiency Below Normal (Bank 1).

Before I decide to spend $700-$1000 for repairs or replacement, I decided to post on here to see if there's anything I could do or look at myself before spending money. I'm still making payments on it so I don't want to spend needlessly when it's something I can do myself. I went on YouTube and it mostly came up with O2 sensors, but it seems like this is just trying the system into thinking it's fine (or legitimately could be bad O2 sensors.) I saw another where a guy poured lacquer thinner into the gas tank at half empty and I looked this up. People claim this worked, but it's mostly on older cars. I'm not willing to pour lacquer thinner into a '09 car I just bought.

Any suggestions?

When you go to Mazda.. they're going to perform a diagnostic and hopefully it isn't the cat.

Faulty catalytic converter
A faulty mass air flow or manifold air pressure sensor
Defective O2 sensor/s
Burnt, chafed, broken, or disconnected wiring and/or connectors
Engine exhaust leak