Help! After exhaust rebuild fault code!

Hi everybody.
I have a 2016 jimny, and recently replaced the choked manifold with a nice branched extractor and new pipe all the way aft, the upper 02 sensor was alway Pre the manifold cat, so I had it put back in to the pre existing port in the new extractor. The. 2 nd 02 sensor was after or just on the lower CAt, so I had a mini cat (fooler) placed on that port, and 02 sensor re installed.
Same day i installed an oiled K and N high flow air filter. I drove well for maybe 40 km and then had fault light. Disconnected battery and reset ECU.
Drive approx 170km and now Have
p0140 code. Which is no activity at 02 sensor bank 1 sensor 2 (which I believe is the sensor with the fooler on it- which was quite expensive!!

I’ve read that this fault code can be produced by oil from pre oiled air filters, but also in changing the exhaust system I could assume that the fooler isn’t working either?

Any experience?
I’d really appreciate some advice here.
Thanks a million!

Your sensor fooler would most likely be a resistor of some sort. There is a different signal from the first and second sensor so not sure if the fooler can be of the same type depending on if you fool the first or the second sensor. Might you have the wrong type?
Anyways not sure i see the point in using a fooler. An aftermarket cat and a sensor is not that expensive.. Especially if as you say the fooler is expensive.

Hey!
The 02 sensor wiring was never disconnected, just sensors removed and re installed, into new exhaust system.
Can I mess around with fooler and or washers, or is there a way to troubleshoot the parameters of the fault?

Hey thanks so much for your replies,
I doubt it, but will have it checked. The shop that did it said it was a first for them and they are keen to help.
If it was a hard fault or a failed sensor I wouldn’t manage 100-200 km between engine check light illumination surely.

I wonder at worst if I can permanently clear that particular code- as the engine runs fine, and much better since free flow

P0140 means the sensor isn't switching*, could be a failed sensor, but I'm a bit suspicious of the fooler.

Is it an extender tube with a little hole in? They are only about £10, and are supposed to work by moving the sensor out of the gas flow, but I don't see what that can do, there is some talk of putting wire wool into the hole in the fooler, again I've no idea what that can do.

Clear the code and see what happens, it seems that a fooler either works or it doesn't. If it is decatted it won't pass emissions test at the tailpipe surely? I'd just refit the lower cat and sensor.

*you wouldn't expect the post-cat sensor to be switching anyway, but I suspect that there is an ecu "test" of the catalyst by looking for a change when it accelerates on open loop and then goes closed loop in steady state- it would expect to see switching from rich to correct under this condition.

Thanks facade,
Good info. Some of its new to me but hope it will help. Surely others have ran into this issue after free flowing the exhaust?

Another question, once the code has logged, does the ECU go into a manual metering mode, or throttle position? Or in anyway throw out fuel economy? I can’t sense the car driving any different.

If not, I’ll experiment with new foolers, as it has to be the weak link, and will maybe look into permanently disabling that code? If there’s a way of doing that

Cheers guys, thanks in advance for any more info

J