Aunt's 02ES has a P0421 code, suggestions?

[run1206]

Hi all,
My aunt has an 02 ES. She's throwing a P0421 code (Warm up Catalyst Efficiency Below Threshold), failed inspection with that code. I'm wondering if she definitely needs a new cat converter or if she might need a new rear O2 sensor or if the exhaust in that section needs replacing.

I'll check google for a bit, but anyone who might know any input is appreciated. Thanks in advance.

[03-Galant-ES]

Hi all,
My aunt has an 02 ES. She's throwing a P0421 code (Warm up Catalyst Efficiency Below Threshold), failed inspection with that code. I'm wondering if she definitely needs a new cat converter or if she might need a new rear O2 sensor or if the exhaust in that section needs replacing.

I'll check google for a bit, but anyone who might know any input is appreciated. Thanks in advance.

My first instinct would be the o2 sensor what is the condition of the gas coming out of the exhaust. Color, smell, smoky?

Is there a chance you can hook up your Rear o2 sensor to see if the code resets itself and go from there?

[run1206]

you mean take my i2 sensor out and put it in her exhaust? a little time consuming but i'll see what i can do

[Galant Evolution]

The 02 sensor is prob not at fault, its doing its job, sensing the cat. How many miles on the car? That code is the 02 sensor telling you the cat isnt within spec. I would replace the cat.

[run1206]

she has over 150K on it. reset the ecu on sunday and the light went back on this morning. Just texted her telling her most likely it's the cat. will see if i can find a site with a good price for cat converters. thanks.

[Galant Evolution]

No problem man