Why wouldn't it? It's downstream of the Cat and measures exhaust gasses..?
The Jaguar diagnostics would tell you what O2 sensor was causing the code, aftermarket read probably would not.
There were a lot of #3 sensors replaced when I was working on them, and only one #1 and no #2s
Theworst ws having to run an overlay harness from Bank 1 Sensor 2 all the way to the ECM for a persistent fault.

 

I had 2 of my 3 replace under warranty in '15 on warranty. no trouble since.

 

I'll probably angle for that, just hope the dealer doesn't throw the usual dealer fit.

 

Update...so apparently I had about half a year of warranty left on it, but their warranty dept tried to upsell me by telling me it expired last year...from which I then splurged on the VAP tune.

They found the tampering and refused to replace the cats. So yeah, fml.

What's weird is that I was told that, at the current state, the P0420 code is "stuck" as in it will always come back even after I replace the cats, and the only way to truly get rid of the code is to replace the ECU altogether. What? I've never heard of a code being permanently "stuck"? Another upsell tactic?

 

Any tune will show up as a “Non-Oem” flag in the ECU. I had one on my 2016 from the VAP tune. It’s up to the dealer whether they report it or not. I’ve never had an issue with my dealer and they replaced the cats when they failed. They could get in trouble if JLR asks for the ECU data dump when they order the replacement parts so is totally up to them to decide to run that risk for you. Cats fail so often on these that I don’t think JLR asks many questions when a claim is made against them.

I believe what they are referring to with the stuck code is the Non-OEM flag. Once it pops I’m not sure if there is a way to get rid of it without a format and dealers can’t do it. Once the cats are replaced the P0420 code will go away.

 

Well my dealership is playing by the rules. According to the notes, the tech sent my non-OEM flag to database so other dealers know my ECU was tuned before I even go there. You're probably right about the permanent code. I'm just going to go with the sport cats...net a little more hp, higher flow and lower temps should be more reliable, not sure if I will like the new sound or not, or if the new steel core is actually better than OEM's ceramic. All the Youtube videos I found is...inconclusive. Poor audio quality makes it hard to judge. I'll be sure to record something better.

 

Every time I’ve had that code it has been because of a very slight vacuum leak on one bank bank one. Everybody always goes immediately to replace the cats but I have brand new cats in my car and I still get that code when I have a very slight vacuum leak at the injector O-rings or at the exhaust pipe connection to the exhaust manifold. The fuel trims look pretty damn good and in my opinion I would think they work perfect but one side is always slightly offset in the In the negative direction as shown on the scanner above so I’m saying you’ve got a vacuum leak. Got the carb clean and start spraying and watch those if you’re trims jump around

 

Thanks for the tip; I already checked the fuel trims and any spikes in lean/rich condition, but they've been pretty smooth throughout. There's also no visible exhaust leaks except at the very very end, past the 3rd O2 sensor, by the axle back, which is ultimately irrelevant. All O2 sensors are also reporting over 99% fuel trim expectations, despite the voltage on Sensor 2 in both banks bouncing up and down rapidly. I don't think there's anything left to check here; the VAP cats are going in. I'll also provide a much better quality recording of the exhaust sound before and after.

 

I want to thank every that contributes to this forum, especially this thread! My 2016 Ftype R AWD threw the 420 code. If it wasn’t for the education on that code that I learned here the dealer may have screwed me over. I started the entire service handoff, witbits throwing a p0420 code. Car was originally sold in California. I have 45k miles and from date of sale 7 more months on my federal and what cal requires on emissions equipment. A day later he called and said parts are ordered and cover under emissions warranty. Not saying they would have, but being a knowledgeable customer might have made them not even try. And it was with a dealer in Austin Texas.