To avoid dealer access to OBD port get one of these:


Then you don't need to reflash stock tune for routine visit. If dealer does need access that will be the only time you need to reflash.

 

@DJS Could you please repost the link to that extended warranty letter? I was trying to download it to send to my dealership, but it looks like the link expired. Thank you!

 

Huh, Dropbox says no expiration date…
https://www.dropbox.com/scl/fi/z4k4i...p6tqui13m&dl=0

 

@DJS Oh nevermind. I was able to access it from my laptop. It was just that Dropbox was blocked on my work computer. Many thanks!

 

So when I asked the dealership technician to just replace the O2 sensor under warranty, he refused saying that the the P0240 code states that the cat is the problem, not the O2 sensor. He said that if it were the O2 sensor, there would be a specific code for the O2 sensor. He said that he would not put in a new O2 sensor because that could be damaged by a bad catalytic converter. That made no sense to me. Is that possible or is he just making this up?

I also sent him this link I found:

"P0420 Code FAQs
How do I clear a P0420 code?
To resolve this trouble code, you must determine its underlying cause and address it.

Can a bad O2 sensor cause a P0420 code?
Yes, it’s one of the issues that can make the catalytic converter inefficient. A catalyst monitor uses signals from the downstream O2 sensor to determine catalyst efficiency. It uses signals from the upstream O2 sensor as a reference point."

P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1) - In The Garage with CarParts.com

Here is the dealership email response to me with the attached pdf on the code:
"Here is the info that we have from the engineers regarding your issue. There are no codes for the o2 sensor; after speaking with the service director, we would NOT be able to change the o2 sensor per your request without a code indicating that is has failed, unless you'd prefer to pay for it. Otherwise, we would have to start with replacing the catalytic converter. "

How should I respond to them?

 

Peronally, I'd be inclined to start with telling GFYS to the service manager and never go back. Buy an O2 sensor, which are MUCH less expensive on the street than the dealership, have it installed by an indie and see what happens. If its the converter, then select from the multiple aftermarket units that have been discussed here.

 

To be fair to the dealer diagnosis, I got the same Cat inefficiency code bank 1 on my '16R after only 13K miles. Still within the full warranty, the dealer first performed the software update TSB, no parts changed.

Code went away and returned in ~1000 miles, the dealer then diagnosed the Cat was bad and replaced under warranty. O2s were not replaced. This fixed the problem, then Cat inefficiency bank 2 appeared in another 2000 miles. Dealer replaced this Cat, no new O2s, and codes have not returned since, currently ~23K miles. My first thought was also bad O2 sensors but turned out the cats were the sole culprit.

If you do replace the cats, replacing both simultaneously makes sense. Also consider: if Jag's extended O2 sensors warranty will still cover you for some time, the dealer may challenge a claim in the future if aftermarket cats, and definitely a tune, were found on the car.

 

The tech is not wrong, changing the O2 sensor for a P0420 is a waste of money.

There's 3 sensors per bank..

The sensor 1 is for lambda control and short term fuel trims
The sensor 2 is to verify the primary catalyst and long term fuel trims
The sensor 3 is to confirm the secondary catalyst and total trims.

By replacing sensor #2 for a P0420, you are assuming the ecu is monitoring faulty values from sensor #2 and ignoring the confirmation of this extra oxygen detected by Sensor #3.

Confirm the software is of the latest calibration (odds are the etch did this), and it's not an issue that can be resolved by replacing sensors. Nonetheless, if you replace an aged sensor, you'll want to replace them in sets (bank 1 + bank 2), otherwise the opposite bank will eventually flag an issue due to an aging factor.

To confirm a fault is with the catalyst, the tech can datalog the downstream sensors and view the voltage. Normally the values are viewed to see if they are mirroring the upstream hego values. However, by having upstream widebands a comparison cannot be done, but just seeing the sensor swinging voltage while hot and at idle is an easy indication of a failed catalyst.

Stock F-Type 5.0L's were blowing through catalysts all the time due to the aggressive stock pops and bangs mapping, hence why years ago a calibration was released to cut the stock pops and bangs duration in half.

 

Thanks Chris, that is the first time I have ever seen an explanation of what the mid-cat O2 sensor (sensor 2) does/monitors/is for, up until now it's been a complete mystery to me!