Burning oil and catalytic converter

The burning oil is probably the source, maybe not. People do not check oil like they used to so get alarmed when it is low. Yours is either coming from the valve seals or a head gasket. You can chemically check for a head gasket leak either with an additive sold at auto parts and a coolant system pressure check. Valve seals do not last forever as they are a rubber product. So if no head gasket leak then replace the valve seals. As far as the 420 code the converter is shot and will need replacing. Normally two things cause that code a bad converter or an air leak in exhaust before converter. The latter rarely happens.

Yep excess oil burning is not a good thing for a converter. It will plug them up and coat the substrate with crud. There are videos on you tube of people actually washing out converters to clean them. Does it work? Do not know, but I doubt it.

But you also want to look at the actual data from the O2 sensors to make sure the catalytic converter is bad before trashing it. You could be seeing a contaminated sensor setting that code.

As for being factory only, yes and no. Because you live in California you have the fun of having the ARB controlling replacement engine parts. They ruled that you have to use either factory OEM parts OR Cal ARB approved parts (I have the same issue in New York). There are about four companies who make after market converters. They get the popular parts that sell certified, the rest they do not.

Even if you got a scanner with live data you really would not know what it means anyhow and I personally do not give recommendations on what scanner product to buy.

There are various "levels" of tools.

The low end tools just read the codes and maybe allows you to clear them. They will not contact the other modules that were not required under the standards. So with those you get P0301 and maybe a definition that it means a misfire detected in cylinder one.
Your Code-Key falls into this area. ($30.00-$50.00).

Next up you have tools that can read the codes from more modules. They also may have limited live data ability. With those you would still get the P0301 but you could go in and see the snapshot data (data that is saved to show what the vehicle was doing when it set the last code detected) As well as being able to see the misfire monitors and other live data like engine temp, throttle position and others.
The Topdon OBDscan+ falls into this group. ($75.00 - $300.00).

Next you get to the lower end pro style tools. These do everything the lower models do, but offer more coverage of modules and live data and some limited abilities with bi-directional control (they can turn on the lights, sweep the dash gauges, reset brake lights and such) Some run on PC with an adapter or are stand alone units.
Something like the AutoXray AX7000 ($400.00-$1000.00) or AutoEnginuitys basic version.

Now you have the tools used in non-dealer shops or as a technicians personal unit in a dealership. These do a lot more than the lower level tools. Giving you access to a majority of the modules and controls for multiple vehicle lines. Plus most have web access and can provide you with links to service sites and help forums as well as programming for the popular modules and some keys.
These are not the typical DIY stuff.
Snap-On Verus or Solus, Macs Determinator, OTC Oncore are in this class. Starting prices of $1,200.00 up to over $10,000.00 for one fully loaded machine.

Last are the true dealer machines. GM Tech2, Tech2 Win, Fords NGS and IDS, WiTech for Chrysler/Jeep are a few of these.
In this class the machines themselves are not real expensive, $5,000.00 to $10,000.00, but they are subscription based. The average price is about $1,200.00 a month for full access and programming abilities. These are the tools when it comes to the makes they support. You can access every module, hidden OEM codes, program anything you need. However, unless you are a dealer and need all that ability it is a very expensive tool.

As for me I have a couple of the second tier units to do quick field scans of auction or used cars just to see what codes may be hiding or if everything is reset, that maybe I should pass.
I also have a Verus Pro and a new Autel that I am playing with. So far they are neck and neck. The big difference is price and support. They each have things they do better than the other.

What would I recommend? That you read up on what you need a tool to do and decide how much do you want to learn about what all the data means. That can take a while.

Awesome explanation of scan tools Steve W. Great job!

Don't let the part numbers throw you. Automakers change the part number if there is a minor update or change for a part, even if it's functionally the same part. So say they took the front converter from your car, decided to use the same engine and converter in a different model. BUT to use it in the new car they needed to weld a tab on to hold a bracket. The new part number will now fit both cars BUT the original part number will only fit yours because it lacks that tab. Another reason they change the number will be if they change part suppliers. They can then track part failures by using the part number. Happens all the time.

Now as to the parts you need.
YES on any gaskets and bolts that are corroded or broken on removal, The gaskets will probably be junk when you remove them but even if they look good they have been compressed and won't seal on the new part.

Which bank - Well for most engines Bank One will be the cylinder head that has cylinder number one in it. In the case of your Honda, that will be the rear cylinder head closest to the firewall. Bank Two would then be the one closest to the radiator.

So if you are seeing the problem on Bank One you need the part to the right in the picture. OR Honda part - 18290RGLA00

You will need at least part numbers 2 and 8. Plus part 18212-SA7-003 which is the gasket between the converter and the pipe.

Now IF all the nuts (17) come off good, and the bolts (15) come apart and those covers (5&6) are good, And you can get bolt 14 out and can get the oxygen sensors out without damage, you should be all set.