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Code P0420 catalytic converter replace

Tiny
PETEJC
  • MEMBER
  • 2007 HONDA CRV
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 80,000 MILES
My son's car has been throwing the error code P0420 for months.
The CEL keeps coming back, always P0420 and only that code.

We did some research and it looks like the catalytic converter.
I found a lot of information on checking the O2 sensors and performed the following tests.
We used a plotting scantool (scantool. Net tool and OBDWiz).


The front censor indicated too lean when opening a vacuum line and too rich mixture when spraying starter fluid in the line as it should.

Just at normal idle the front sensor seemed okay, but the back sensor keeps oscillating. See the attachment.

If I understand things correctly Bank1 Sensor 2 should be a steady 0.5 volts.

If that is correct then is the oscillation caused by the catalytic converter failing to do its job or can it be something else?

If it is the catalytic converter, it might be easy to swap for a new one but I am concerned about the two bolts holding the front of the catalytic converter. They seem pretty small and have been "cooking" for over ten years. The heads might be easy to rip off.

Has anyone changed a catalytic converter and can you tell me if my concerns are valid?

Thanks in advance.

Pete
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Friday, February 23rd, 2018 AT 6:59 PM

5 Replies

Tiny
STEVE W.
  • MECHANIC
  • 12,973 POSTS
Your testing and ideas are correct. The rear sensors should remain steady, they may rise and fall a small amount as the volume of exhaust gases past them changes but they should not track the front sensors like yours is if the convertor is working. So yes you need to change the convertor.

As for the converter hardware, your concern there is also valid. The bolts thread into the manifold and can become permanent residents with time. My normal process in the shop is simple. Hit the head of the bolt a couple times to knock the rust off. Then hit the treads on the upper side of the manifold with a wire brush (or if there is a lot sticking out I will cut them off to avoid dragging all the rusted threads through the hole. Then I heat the manifold around the bolts. Rub a candle on the part of the bolt on top of the manifold so the wax can work its way into the threads, Then try to remove the bolt. In this an impact is a good thing. If you have air tools they are great, or buy one of the 3/8 drive cordless tools. I know folks who use the Earthquake units from harbor freight daily and they are holding up. But that is your prerogative. The impacts will 99% of the time break them free and back them out.
Get new bolts and springs to install the new unit. If you are not in New York or California it is your choice what you use as a replacement however most folks discover that the aftermarket units do not last like the OEM's and the same code returns.

One thing you will also want to do is clean the throttle body and make sure the truck is not burning oil or excess fuel as those will ruin a converter quick, as will coolant usage. I say that because 80,000 is a short life for a converter.
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Friday, February 23rd, 2018 AT 9:59 PM
Tiny
PETEJC
  • MEMBER
  • 3 POSTS
Steve,
Thanks for your prompt and very informative response.
As for the bolt removal, that is exactly what I do (have done) except I never thought of the wax idea, great!
I have a 3/8 cordless impact tool so I can put that to good use.
I see the bolts at RockAuto and they come with nuts. Maybe the car has nuts, maybe the bolt kit is "universal" and includes nuts whether needed or not. Nuts would make me happy because if I twist off a bolt head I should be able to drive out the remaining bolt part. I need to get a better look at the car.
Your diagram shows a ring between the manifold and the catalytic converter. I cannot find that at parts stores for this vehicle. Is the diagram generic or specific to this car?

The early failure of the catalytic converter bothers me also. But the engine runs great. Smooth idle, no hesitation under max acceleration, no oil use (to speak of) or coolant loss.

We are in Tennessee but in one of the only five counties that require an emissions check. All they do is hook up a scan tool to make sure the CEL is off and the tests have been run (in case the CEL was just reset). Then they check that the gas cap holds pressure and run a mirror under the vehicle to make sure no one removed the catalytic converter.
Also, there is talk that the legislature is considering doing away with the emission test requirement.

Just a point. I am getting the feeling that there is more to a Honda P0420 code then the public or bottom end scan tool makers know about. I can find sites where there are over one hundred threads about P0420 and almost never any other codes. Hard to believe there are not other codes. Maybe there are but you have to take it in to the dealer for a full repair and only they can access the other codes.

Thanks again.
Pete
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Saturday, February 24th, 2018 AT 9:27 AM
Tiny
STEVE W.
  • MECHANIC
  • 12,973 POSTS
That is the diagram for an 2007 CR-V. The ring is the gasket. Look under pipe flange gasket/seal on rock auto. The OEM front bolts are threaded into the manifold, no nuts, they include the nuts in case you need to drill out a broken bolt.
The P0420 code is a pain. It usually occurs by itself because it is one of the few codes that does actually tell you which part is bad. Unlike a P0301 (misfire cylinder one) where it could be the coil, plug, wiring, ignition module, bad valve, low compression, internal gasket leak or bad piston. The P0420 is just, hey the converter is not working.
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Saturday, February 24th, 2018 AT 2:19 PM
Tiny
PETEJC
  • MEMBER
  • 3 POSTS
Steve,
You were a great help. But my son has been procrastinating, driving an unregistered car. But with a 90 day grace period that ran out March 15. I kept offering to help him with the repair but, if you have kids (this one is 34 years old) you might know what it is like.
Well, Friday he started driving and saw that the CEL was off so he zipped into the inspection station and passed all tests. Today is Monday, the light came back on.
No way would I have luck like that.
Kids?

Thanks Again,
Pete
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Monday, April 16th, 2018 AT 7:22 PM
Tiny
STEVE W.
  • MECHANIC
  • 12,973 POSTS
Well there is the saying about being lucky or good. He must have found the luck part somewhere. My luck usually runs the opposite way.

Well if you're lucky he'll replace it before the next inspection.

You are welcome. Come back anytime with your automotive questions.
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Tuesday, April 17th, 2018 AT 2:14 PM

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