2015 QX80 catalytic converters

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Hello -
I just purchased this from a law enforcement guy whose FIL owns the dealership. It has 155k miles but the selling point was the binder he gave me filled with every service record. Plus he gave me a good deal.


After 1500 perfect highway miles I recently took it to dealership to have oil changed, tires rotated and have a 100-point analysis done on it. ALL WAS WELL.


I drove it off the lot. The next morning the MIL light comes on solid and took it back to the dealership. I'm now told the "codes indicate BOTH catalytic converters need to be replaced..."


After asking a few questions I'm told it's ok to drive 1000 miles on it (I had another upcoming trip). I call up a different dealership (that the previous owner had do all his service on it) and gave him the vin#. I ask him if maybe the sensor itself or whatever is signalling codes to the computer might be checked first before shoveling $8+k into the car. He talked around it a bit--focused his response on the full cost of diagnostics vs that cost being waived if I have the work done that the diagnostics suggest.


I drive mostly highway miles and although I don't know this car well yet it seems like it still drives the same but mileage gauge now sits consistently 16.9 vs 20+ that I was getting. (really...16,9? not 16.8 or 17.2) I drive with the mileage economy status window on that shows it fluctuating between 0 and 30 and it's at or very nearly 30 the entire time except when shifting gears (I'm in very flat country). While I'm not as concerned about mileage as I am about the care and maintenance, it is disconcerting.


Before buying I looked into QX80 issues and know that "things can happen" at this age and miles, etc. However, with all the catalytic converter drama the past few years, and this problem popping exactly right after it was serviced at a place new to me, I'm frustrated and a bit dubious.


Please share your thoughts and suggestions. Thx

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ALSO --
I don't know if other codes were tripped--just going by the receipt I was given for the inspection.

The typical dlrshp service receipt indicates (comparing these to other receipts provided by the previous owner):

"Upon inspection of veh tech found 2 codes present for P0420 and P0430. Based on codes present technician recommended replacement on catalytic converter"

However, attached to the dealership receipt is another printout with no company header/info--just blank, identifies 3 names for "service Advisor" (w/ dlrshp email), "Parts Personnel" (w/ dlrshp email) and "Service Technician" (who is also ID'd on the dlrshp page but is listed with only a personal gmail address...)

and the quote reads, "Exhaust Catalytic Converter Replacement: P0420 and P0430 are tripped showing internal failure in both catalyst systems."
Itemized list includes two manifolds at $1500ea; 2 exhaust gaskets, one man exhaust gasket and two front exhaust tubes at $1500 ea.

A second page behind this one DOES have a dealership info at the bottom and has a quote for a broken door latch.

Thank you for that explanation. I have read other threads and you have mentioned those points, which I now understand better in context. I purchased some cataclean and will add it pretty soon. I feel frustrated by the sequence of events, since the codes tripped literally less than 24 hrs after driving the car off the lot.

My (limited) understanding is that the cats increase performance, fuel efficiency and exhausted air quality although my car does not require inspection in this part of the country. I'm curious how to determine decreased performance? Are the cats just losing performance and efficiency or are they actually clogged? Shouldn't the sensors and/or the O2 sensors be evaluated? Shouldn't the temp of the inlet + outlets be measured or back pressure test be evaluated first before replacing them? Or would these steps not align w/ garage protocol of the dealership?

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Input temps compared to output temps usually are a good indication of cat efficiency, out put should about 125 degrees more than input, fully warmed up.

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Thank you. I can't do this myself but will find someone who can.

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Are there any other ways to investigate the true condition of a cat (bad warning light vs. a clogged cat?)



What is the likelihood that both went bad at the same time?


Since my previous post I added some cataclean, which immediately cleared the codes/MIL light. Days later, I was driving through a cemetery and accidently drove over a small branch and thought it might have knocked the undercarriage and either immediately or later that day the MIL light came on again. I've added two more bottles of cataclean and the light is still on - never went off again. I'm now on the road and I am worried it might not be a good idea to drive another 500 to get back home to get the issue handled.

Thanks for your responses.