Code P0420

Asked by Michael 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
101,575

KenF answered 5 years ago

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.

2 people found this helpful.
Mark helpful

Your Answer:

Related Questions

  • Code P0420 1 Answer

    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...

    2004 Toyota Corolla

    -

    Maintenance & Repair

  • p0420 code and stalling 5 Answers

    When I first bought this car a year ago I had a light come on for p0171 for lean condition, so this is what I have done. I changed the o2 sensor before the catalytic because this is what I was told...

    2004 Toyota Celica GTS

    -

    Maintenance & Repair

  • P0420 code 1 Answer

    P0420

    2005 Pontiac Grand Prix Base

    -

    Maintenance & Repair

  • What else causes Trouble code P0420? 1 Answer

    Replaced both O2 sensors with Denzo oem. Replaced cat with toyota oem. No exhaust leaks. Reset computer. What else could cause the P0420 code?

    1995 Toyota Tacoma 2 Dr STD 4WD Standard Cab SB

    -

    Maintenance & Repair

  • Check Engine + VSC = Code P0420 2 Answers

    I recently purchased this car, and today the check engine light and VSC came on. I had Advance Auto scan it and it came up with P0420. What are some troubleshooting steps I can do before taking it ...

    2004 Toyota Highlander V6 AWD

    -

    Maintenance & Repair

Shortcuts

Search Toyota Corolla Questions

CarGurus Experts

  • #1
    Jeff Polhemus
    Reputation
    3,360
  • #2
    Gene Arnett
    Reputation
    3,270
  • #3
    hashimmir
    Reputation
    2,500
View All

Find great deals from top-rated dealers

Search

Related Models For Sale

Used Toyota Camry
44 Great Deals out of 1,134 listings starting at $4,795
Used Honda Civic
192 Great Deals out of 4,047 listings starting at $440
Used Honda Accord
57 Great Deals out of 961 listings starting at $2,995
Used Toyota RAV4
127 Great Deals out of 3,065 listings starting at $4,999
Used Honda CR-V
181 Great Deals out of 5,013 listings starting at $440
Used Toyota Tacoma
37 Great Deals out of 728 listings starting at $9,975
Used Hyundai Elantra
164 Great Deals out of 3,045 listings starting at $1,995
Used Toyota Prius
14 Great Deals out of 196 listings starting at $2,028
Used Mazda MAZDA3
71 Great Deals out of 1,303 listings starting at $3,499
Used Nissan Sentra
69 Great Deals out of 1,873 listings starting at $190
Used Toyota Yaris
14 Great Deals out of 191 listings starting at $2,449
Used Nissan Altima
25 Great Deals out of 676 listings starting at $3,795

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.