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

42,815

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 85,965 nationwide Camry listings starting at $1,296.

ZIP:

Toyota Camry Experts

  • #1
    Reelin68
    Reputation
    14,040
  • #2
    Tom Demyan
    Reputation
    4,770
  • #3
    tenspeed
    Reputation
    3,060
View All

Related Models For Sale

Used Honda Accord
1,094 Great Deals out of 71,806 listings starting at $850
Used Toyota Corolla
934 Great Deals out of 63,275 listings starting at $1,850
Used Honda Civic
773 Great Deals out of 60,518 listings starting at $950
Used Nissan Altima
1,270 Great Deals out of 77,668 listings starting at $1,695
Used Toyota Avalon
239 Great Deals out of 15,912 listings starting at $1,195
Used Toyota RAV4
804 Great Deals out of 50,805 listings starting at $1,600
Used Hyundai Sonata
878 Great Deals out of 56,111 listings starting at $1,500
Used Toyota Highlander
575 Great Deals out of 35,686 listings starting at $2,500
Used Nissan Maxima
317 Great Deals out of 21,702 listings starting at $999
Used Honda CR-V
840 Great Deals out of 58,481 listings starting at $1,495
Used Toyota 4Runner
344 Great Deals out of 26,026 listings starting at $1,800
Used Toyota Tacoma
652 Great Deals out of 45,099 listings starting at $2,500
Used Toyota Prius
336 Great Deals out of 15,689 listings starting at $999
Used Chevrolet Malibu
1,035 Great Deals out of 60,988 listings starting at $880

Used Cars For Sale

2018 Toyota Camry LE For Sale
16,220 listings starting at $19,489
2017 Toyota Camry LE For Sale
21 Great Deals out of 1,206 listings starting at $13,500
2016 Toyota Camry LE For Sale
28 Great Deals out of 1,826 listings starting at $9,950
2015 Toyota Camry LE For Sale
51 Great Deals out of 1,542 listings starting at $9,500
2014 Toyota Camry LE For Sale
69 Great Deals out of 1,270 listings starting at $6,995

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.