p0420 Code is back after replacing CAT

Asked by Nov 10, 2015 at 11:43 AM about the 2001 Toyota Camry LE

Question type: Maintenance & Repair

About 5 months ago at 140K miles I had the downstream CAT replaced with
an aftermarket one because of the P420 Code.  The check engine light
went away.  3 Months ago at 143,700 miles I had the flex pipe crack and
had it immediately replaced with a new one.  Now at 148K Miles I have the
P0420 code back.  I took it back a few days later to the shop to have them
inspect the weld on the flex pipe because it runs a slightly louder than
before.  They said everything checked out.  I'm wondering if the flex pipe
replacement could have any thing to do with the code coming back.  

Can someone help me trouble shoot this?  I know there are several
possible causes and I don't want to just replace parts, I'd like to find root
cause.  Thanks in advance for any insight.

4 Answers

41,915

A bad O2 sensor will trigger the code as well. I would suspect that the one on the upstream side is bad. If you want to pay to have them check the sensors with a scope, that's an option. You will still be stuck paying for labor. The unfortunate part is, you can't figure out what's bad until you replace it. Unless you pay for the tests.

The fact that the engine sounds "louder" than usual tells me you need a second opinion and a full inspection of the exhaust system on this vehicle. Also, it would be nice to hook up a scan tool which is capable of displaying "Live Data" such as O2 sensor function. IMO...after market parts...especially...CAT's.....are not my first choice when replacing parts. I would be inclined to clear this code...road test he vehicle and see how fast the code comes back. Then ...a scan tool inspection will provide data detailing what was going on just before, during, and after the computer set the code. This diagnostic procedure should lead one to conclude the root cause for this issue.

I did reset the code and it came back on within the first 25 miles. I think I'll take it to a shop and pay $100 to have them monitor live 02 data.

Sounds like a plan. If they decide to road test this vehicle, you might suggest they take the scan tool with them which will allow them to collect DATA when the event occurs.

Your Answer

Camry

Looking for a Used Camry in your area?

CarGurus has 81,486 nationwide Camry listings starting at $999.

ZIP:

Toyota Camry Experts

  • #1
    Reelin68
    Reputation
    13,680
  • #2
    Tom Demyan
    Reputation
    4,680
  • #3
    tenspeed
    Reputation
    3,030
View All

Related Models For Sale

Used Honda Accord
969 Great Deals out of 59,135 listings starting at $1,099
Used Toyota Corolla
755 Great Deals out of 54,178 listings starting at $1,500
Used Honda Civic
738 Great Deals out of 68,782 listings starting at $1,350
Used Nissan Altima
974 Great Deals out of 77,792 listings starting at $1,695
Used Toyota Avalon
221 Great Deals out of 16,824 listings starting at $1,499
Used Toyota RAV4
675 Great Deals out of 45,921 listings starting at $1,195
Used Hyundai Sonata
715 Great Deals out of 50,449 listings starting at $1,995
Used Toyota Highlander
449 Great Deals out of 30,974 listings starting at $2,500
Used Nissan Maxima
254 Great Deals out of 22,716 listings starting at $1,400
Used Honda CR-V
718 Great Deals out of 56,944 listings starting at $1,200
Used Toyota Tacoma
543 Great Deals out of 44,361 listings starting at $1,790
Used Toyota Prius
303 Great Deals out of 16,022 listings starting at $1,200
Used Toyota 4Runner
277 Great Deals out of 23,164 listings starting at $2,300
Used Chevrolet Malibu
932 Great Deals out of 64,910 listings starting at $1,995

Used Cars For Sale

2018 Toyota Camry LE For Sale
16,214 listings starting at $20,102
2017 Toyota Camry LE For Sale
10 Great Deals out of 1,332 listings starting at $13,495
2016 Toyota Camry LE For Sale
44 Great Deals out of 1,704 listings starting at $10,980
2015 Toyota Camry LE For Sale
31 Great Deals out of 1,339 listings starting at $10,499
2014 Toyota Camry LE For Sale
71 Great Deals out of 1,614 listings starting at $7,990

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.