Code P0420

Asked by Feb 26, 2019 at 11:56 AM about the 2004 Toyota Corolla

Question type: Maintenance & Repair

I'm working on my '04 Corolla (114k miles) which
is throwing code P0420 (catalyst system efficiency
below threshold bank 1). I suspect that it is just the
O2 sensors that may be bad rather than the whole
converter. I have not noticed a strong odor from
the exhaust, nor loss of power, and it's getting
around 35mpg hwy. Should I try to just do the O2
sensors? Is there a more reliable way to identify if
the issue is the cat or sensors?

1 Answer

59,045

An O2 sensor is a lot easier and cheaper to check or replace than buying a new catalytic converter. You may also want to look for any exhaust leaks, leaking injectors, or timing, as those can also trigger a PO420 code. You can Google "how to test O2 sensor" and "how to test catalytic converter", but just so you know getting an O2 sensor out of the exhaust can be a challenge for a home based DIYer. There's a video on Youtube as well on checking catalytic converters for blockage using a shop vac. Most likely your problem is going to be with the sensor or one of the other issues listed above and not with the cat.

Your Answer:

Toyota Corolla Experts

  • #1
    F_O_R
    Reputation
    2,580
  • #2
    Jeff Polhemus
    Reputation
    2,370
  • #2
    tennisshoes
    Reputation
    2,370
View All

Find great deals from top-rated dealersTM

Search

Related Models For Sale

Used Toyota Camry
49 Great Deals out of 1,483 listings starting at $3,495
Used Honda Civic
149 Great Deals out of 6,385 listings starting at $1,295
Used Honda Accord
53 Great Deals out of 2,151 listings starting at $1,850
Used Toyota RAV4
85 Great Deals out of 4,561 listings starting at $3,888
Used Hyundai Elantra
115 Great Deals out of 5,172 listings starting at $1,900
Used Nissan Altima
43 Great Deals out of 1,493 listings starting at $1,900
Used Nissan Sentra
47 Great Deals out of 1,965 listings starting at $1,495
Used Honda CR-V
113 Great Deals out of 6,819 listings starting at $3,600
Used Toyota Yaris
19 Great Deals out of 791 listings starting at $2,495
Used Toyota Prius
10 Great Deals out of 472 listings starting at $2,995
Used Mazda MAZDA3
43 Great Deals out of 3,795 listings starting at $1,995
Used Toyota Tacoma
26 Great Deals out of 1,425 listings starting at $7,900
Used Toyota 4Runner
17 Great Deals out of 760 listings starting at $5,995
Used Toyota Highlander
26 Great Deals out of 1,659 listings starting at $3,555

Used Cars for Sale

2020 Toyota Corolla For Sale
3,823 listings starting at $18,990
2019 Toyota Corolla For Sale
10 Great Deals out of 293 listings starting at $18,165
2018 Toyota Corolla For Sale
15 Great Deals out of 278 listings starting at $14,544
2017 Toyota Corolla For Sale
39 Great Deals out of 312 listings starting at $12,495
2016 Toyota Corolla For Sale
9 Great Deals out of 437 listings starting at $8,995

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use. Content will be removed if CarGurus becomes aware that it violates our policies.