P0420

[Scoop]

My wife drives an 5.4l 07 Expedition with 100,000 miles. She told me the check engine light was on and it was running bad and that there was a fuel smell coming from the tail pipe. I brought it to a locale auto parts store and it was showing a miss fire on #3 cylinder. I changed the coil pack and the truck is running better we put a couple hundred miles and the light never cleared. I brought it back to check the code now it's showing a P0420.
I've been told that unused fuel is a big reason that a catalytic converter will go bad. I've also seen where the oxygen sensor could be the problem. My question is should I change the oxygen sensor if so which one should i change or should I change the catalytic converter? If it's the converter do i change the smaller or the bigger one.

 

[flyin]

Palidinmicro.com. look for o2/mil eliminator, diy mil eliminator. 5 dollars and you are good to go as long as you cat isn't plugged. It works

 

[RTX 17]

My wife drives an 5.4l 07 Expedition with 100,000 miles. She told me the check engine light was on and it was running bad and that there was a fuel smell coming from the tail pipe. I brought it to a locale auto parts store and it was showing a miss fire on #3 cylinder. I changed the coil pack and the truck is running better we put a couple hundred miles and the light never cleared. I brought it back to check the code now it's showing a P0420.
I've been told that unused fuel is a big reason that a catalytic converter will go bad. I've also seen where the oxygen sensor could be the problem. My question is should I change the oxygen sensor if so which one should i change or should I change the catalytic converter? If it's the converter do i change the smaller or the bigger one.

Thought I'd bring this back up as I'm having this code with my 05. A couple months ago I had one of my injectors go and was replaced but since then this code Po420 has come up. I had my mechanic clear the code so I could get my inspection sticker, it did pass. Can i continue to drive the vehicle with no worries? I got some prices for the right bank cat...ouch. Any possiblity it may be just an O2 sensor and how many are there on each bank?

I really don't like having the CEL light on and not knowing if another problem comes up for the car. thanks Doug

 

[RTX 17]

Anyone have an idea?

 

[dougmcp]

If the code comes back then you need to address the problem.
The P0420 code comes from the rear O2 sensor on Bank side 1.
This could be a bad sensor or the cat coming to the end of it's life.
Depending on your smog readouts and the restrictions in your state it may even be fixed by installing an O2 extender (spark plug antifouler) between the O2 sensor and the pipe. It's a $5 item and takes 10 minutes to do.

They look like this:

 

[RTX 17]

If the code comes back then you need to address the problem.
The P0420 code comes from the rear O2 sensor on Bank side 1.
This could be a bad sensor or the cat coming to the end of it's life.
Depending on your smog readouts and the restrictions in your state it may even be fixed by installing an O2 extender (spark plug antifouler) between the O2 sensor and the pipe. It's a $5 item and takes 10 minutes to do.

They look like this:

Yes this same code keeps coming back. So I'm assuming that the right bank which is the side that the injector failed on is not doing it's job now and needs to be replaced OR it may be just the O2 sensor? So it's the rear sensor to start with correct? Doug

 

[dougmcp]

The front O2 sensor sets the mixture and the rear O2 sensor checks the cat efficiency.
If an injector failed and was replaced but it's not throwing a rich/lean code and just the P0420 then it points to the rear O2 sensor or cat.

With a bad injector you could have coated the cat to the point where it is not doing it's job anymore.
You could try cleaning the O2 sensor, if that fails, adding the O2 extender will keep your CEL from coming on but if your cat has failed you may fail the next smog check.

 

[RTX 17]

The front O2 sensor sets the mixture and the rear O2 sensor checks the cat efficiency.
If an injector failed and was replaced but it's not throwing a rich/lean code and just the P0420 then it points to the rear O2 sensor or cat.

With a bad injector you could have coated the cat to the point where it is not doing it's job anymore.
You could try cleaning the O2 sensor, if that fails, adding the O2 extender will keep your CEL from coming on but if your cat has failed you may fail the next smog check.

Ah thanks now I see. So yes with the PO420 code only, my cat is def. no good, but by adding the extender will get rid of the CEL. ok. Next question it's not rocket science to install the o2 extender? A local autoZone has them. Does it have to be drilled and tapped or does it go in one of the O2 ports? Sorry never heard of these. Thanks, Doug

 

[dougmcp]

The extender/antifouler has the same threads as your O2 sensor and goes in between the sensor and the pipe.
You unscrew the O2 sensor, screw in the extender then screw the O2 sensor into the extender.
I had to do the ones on my V6 Passat because of an oversensitive computer.
The motor was out at the time but here's what they looked like:

 

[Scoop]

Here's an update on my problem. I changed the converter, coil packs and the down stream O2 sensor on my wife's 2007 Expedition. She calls me at work tonight and tells me that the check engine light came back on so I advised her to go run to AutoZone to get it scanned and it's still showing a P0420 code. Should I have also changed the bank 1 upstearm O2 sensor or would that throw a different code? I'm about to go slap crazy trying to figure this out so if anyone could give me some ideas on what step to take next I would greatly appreciated it.