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New catalytic converter and 02 sensors - 2005 Ford Mustang

I recently bought a 2005 Ford Mustang GT. It has 87k miles on i , the mechanic I had check it out said that it appears in good shape. However, it had a straight exhaust put on because the previous owner didn’t have emissions in his county and enjoyed the sound. So, on the condition that the dealer put a catalytic converter put on, i agreed to purchase the vehicle. It’s a bolt on converter as opposed to welded, so I assume it’s after-market - the receipt is pretty vague. Anyway, I drove it back to my town about 2 hours away and the check engine light came on. I went to autozone and got the code P0161 saying it’s the 02 sensor - bank 2 sensor 2. looking at the description it looks like it’s not much of a big deal. The dealer is of the mind that the sensors are good. What do you guys think? it’s downwind, so is it just not getting along with the new Cat? Also, I have to pass emissions, will this impede me passing? If it’s a matter of living with the check engine light I bought my own scanner to keep an eye on new issues. But I’d rather not have the Cat die a slow death either. Lastly, the car seems to drive fine, the MPG seem to be about average.

I think whoever put the cat on is responsible for getting it right. They took a major gamble trying to get this car back in compliance, who knows what else was/is wrong with it. But you’ll have a long drive to get it back to them.

All catalytic converters are not the same. I would have made the dealer put an OEM cat on it, not just “a” cat. They probably installed the cheapest one they could find, and now this is the consequence.

I did some research on the part. apparently it is OEM.

It is possible it has nothing to do with the new cat. From your link

Possible Solutions

Replace HO2 Sensor
Repair open or short in power circuit
Repair open or short in ground circuit
Repair damaged connector due to tracking

Maybe a wire got compromised during install. In our state you would fail emissions test.

With the CEL on, you will not pass an emissions test…Mustang GT’s (V8) have two converters, not one…I would have a Ford Dealer scan the ECM to be sure it has the correct EPROM (chip) in it. The former owner might have done more than just remove the converters…

Most states have laws making it illegal for a licensed Dealer to sell a car with a tampered emissions control system…It’s a Federal offense to tamper with an automotive emissions control system…The former owner might think removing the converters was great sport, but it was illegal and if push comes to shove, he is on the hook …

thanks for the help, y’all. dealer replaced both downstream o2 sensor and scanner now reads clear. and watching and talking to their mechanic, I’m pretty sure I know how to do all 4 in the future. drove it around, started a few new drive cycles and still read clear. I bought my own scanner, too, for the future.
I’m going to follow up on the ECM with a ford dealer, though. sounds like a good way to cya.