New catalytic converter, covered under warranty.
So really, I'd only had the car a couple of weeks when the transmission crapped out, but until it did, I hadn't seen a CEL. After getting the service done for the new input shaft seal, new clutch pack, new TCM, etc. I barely made it home before the P0420 popped up. I got the same code on my old Honda (Nearly 3X the mileage on that one.) If I reset the fault codes using Torque, they stay off for a month or more before they trigger again.
So, I reset the codes, under the (apparently mistaken) assumption that there would be no warranty on the catalytic converter. I didn't make it in to work before they popped up again. Reset, didn't make it back home again. This is about a 25km(16 mile) commute, about half of it on the highway.
P0420 is a catalytic converter under-performing, so unless the failure is hard and absolute, then one would expect to see a gradually increasing frequency of check engine lights for the P0420 code over time, and this seemed rather sudden, and also immediately following other work on the car.
The mechanism for this code is typically too much oxygen still in the exhaust downstream of the catalytic converter. If one assumes that the overall air/fuel mix is appropriate (as measured by the O2 sensor upstream of the catalytic converter) then post catalytic converter there should be near complete combustion, resulting in almost no O2 left.
Certain seals can leak such that they allow outside air to be drawn into the exhaust system upstream of the O2 sensor, or the O2 sensor can be installed in such a way as to not exclusively measure the exhaust gasses, and get contamination from outside air. Exhaust flex pipes can also leak in this manner. this will trigger P0420, as there is then too much O2 in the measured sample, even though the catalytic converter is still doing its job perfectly well.
Now, I haven't spent a lot of time underneath this car, and so I don't really know exactly how everything is connected, but in order to remove the transmission, at least motor mounts must be disconnected. In the Supra (Which is of course rear wheel drive) you can't drop the transmission with the exhaust in place, and even disconnecting the motor mounts, it is recommended to disconnect the front exhaust in order to prevent excessive strain on the hangers and pipes. Maybe the transmission in this can be dropped without disturbing the exhaust at all, but it seemed a more than reasonable hypothesis to explain both the timing and severity of the failure.
Replacing the catalytic converter is still a valid treatment, particularly if Ford will then pay for parts and labour. The dealership would have had to cover everything if they let it be about something that they did wrong, so even if the tech found a problem, I doubt that I'd have heard about it.
However, in the end, it was covered under warranty, even if it did mean that I spent another week with a service loaner until they got around to doing anything with my car. From that perspective, I can say that at least Ford Canada is willing to cover the catalytic converter for a 2012 with about 121,000 kms on it. I think that they checked that it would be okay with 130,000 kms on it, so I was probably on my last 6 months of warranty with my annual mileage. Now it's a new unit, so I will probably not see the end of service life of this one.
