Hello MDX side of Acurazine.

My mom has an 08 MDX (165,000ish miles) and it threw a P0420 code a couple weeks back. I cleared the code and yesterday it came back. I understand that P0420 (Catalyst System Efficiency Below Threshold (Bank 1)) is the code that says the cat isn't working as it should, but that is determined by the O2 sensors which will give erroneous readings if they fail.

Has anyone had experience with this? I'm thinking to start with the O2 sensors and if that doesn't fix the problem then that points to the cat. I'm aware there are multiple catalytic converters and banks of O2 sensors. Which is bank 1? I assume replacing the O2 sensor is pretty DIY-able. Please correct me if I am wrong

TIA

 

There is a photo, of the lay-out, about mid-way down.

2007 mdx: 000 miles..cel code p0420 bank 1 comes on intermittently..v6

Are you in a city where an emissions test is required, to get new tags?
With that P420 cel, your computer thinks that you need more gas, in the fuel to air mixture ratio. Expect to see your mpg to drop below 12.

 

Thank you. Yes, an OBD II emissions test is required to renew the registration in my county.

So what I gathered from the conversation in that link is that an O2 sensor will do no good for the p0420 code and that its the rear cat that's gone bad. But the cat does not have any sensors to determine whether it is still functional..That is handled by the O2 sensors, correct? That is my understanding, and by that logic it makes sense to start with the O2 sensors, swap front and rear banks (if that is possible) and see if the code follows to bank two or if it stays in bank one, rather than replace the cat for hundreds of dollars.

Does anyone have experience with this code? Please correct my thinking if I am wrong. I haven't had to mess with the emissions system before

 

Watch the oil level. If you are adding 1 qt every 1300-ish miles, it will cause the cat to fail.
A newer engine with great rings and valve stem seals doesn't let any oil get past, so no oil goes towards the exhaust system.
When oil does get past those rings and seals, it clogs the catalytic converter(s).
With a cat not (filtering) cleaning the exhaust smoke, the secondary O2 sensor(s) change their voltage level and report back to the car's cpu. The program sees too much oil in the mixture and adds more gas.
Your mpg will go down.
If you're not burning oil and your mpg has not gone down, it is good to start with the O2 sensor(s).
Note...If you can not accelerate onto a on-ramp, like you can't go over 40 mph, then your cat is so clogged that it requires immediate replacement.

 

You need to buy Spark Plug Non-Fouler.
Remove lower oxygen sensor, take these two Non-Foulers screw them in to the CAT and then install oxygen sensor back. Reset the code and it should never come back, if it is not coming back, you will probably want/need to replace CAT.
Link for Spark Plug Non-Fouler
VVVVVVV

 

Though this will work (and you could get an angled O2 adapter, from eBay) the emissions certification shop will see it and fail you, when they put the car on the rack to listen for leaks.

 

There will be no leaks.... Have you done it? Why you claim there will be leaks?

 

As part of the emissions inspection, the tech must visually inspect the exhaust piping, for possible leaks and tampering.
I'm not saying that your foulers will leak.
I'm saying two things
1 a weld/seam may be leaking and the tech can not hear it, unless he is close to it, so the car is put on a rack and the pipes are inspected, with the engine running.
2. Foulers and angled O2 adapters are considered to be tampering and the tech will fail the car.

Finally, yes I clogged two cats, used the angled adapter, and decided to replace my engine, for half the cost of rebuilding it.
When I get home I'll copy the link, to that project.

 

Ok, I had to replace the cat, to pass emissions inspection.
6 months later that OEM cat was clogged.
I bought another OEM cat and started looking into fixing my oil consumption issue.
Here's that project:

NonVtec Honda Forums ? View topic - B18B1 is out and a B18B is in, parts list & photo

 

Thank you all for the info. I'll check the oil, and relay the info about the non-foulers to my mom. The car is driving normally and MPGs don't appear to have dropped by any significant level.

I live in Texas, so the emissions test isn't that extreme. The tech simply plugs a computer into the OBD port and checks for codes and "readiness monitors". There's no real inspection of the exhaust system. The emissions test is just simply an OBD II test. (If the car was pre-OBD II then it's a bit more in-depth, but thats not the case here)