New to forum and have an o2 sensor problem

Hi all, I have a 2015 abarth 500 w/77k on it and it threw a p0140 code for the o2 sensor. The code is for no activity o2 sensor bank 1 sensor 2...so I replace the downstream sensor and after about 2 days starts repeatedly throwing a p0137 code (undervolt of same sensor)...is my CAT shot then? Or might I have a bad sensor out of the box? I'm using a Bluetooth obdII reader and it's showing exhaust temps around 1700 at wot which doesn't seem too abnormal to me for a turbo engine but I'm not sure hence the post... Any input would be much appreciated, and thanks in advance for taking the time to look.

First re check the connection pull apart and re join
Post cat sensor I'm assuming, doubt its anything to do with the cat, how much was the lambda sensor a rough check here shows about $160, was it a genuine plug and play sensor?
Note the American engine is somewhat different to here.

First off thanks for the reply, it was a plug and play i didnt have to wire it, i paid around $60 for it the upstream would have been around there at 100 more but as I believe it is a mopar part number we get them cheaper here... I reconnected a few times and the sensor does respond, though at a low voltage, the air fuel ratios are ok as well, so far as I can tell...the only thing that might lead me to think maybe it's the cat is that I was victim of a freak accident a few months back where a piece of carbon or something got smashed between the exhaust valves of one cylinder, causing full compression loss and melting the spark plug...so in theory combusting fuel may have touched the cat...exhaust and turbine housing was clean but doesnt mean there wasnt damage, but i got the valves fixed and for around 10k miles all was well

Thing is the cat even if faulty should not create a under voltage sensor reading, given the under volt was not there with the broken sensor, I'm just a bit suspicious of the new part? Just a thought?

I'm not saying it's not possible, all made by the lowest bidder... I reset the code and applied some dielectric grease to the connector, and it's giving more consistent readings so I'll see if it trips again