Fault Code P0130, front or rear???

[Gti_fly_bye]

Hi all, I've been on the forum since I bought my wife a A3 1.6 8L with only 90k on back in March and found lots of answers on here, great work!

So far its had, a new battery, new hazard light switch, new brake disc and pads, can belt and water pump, some 16" oem sport alloys and I've vinal wrapped the dash trim where the soft touch was peeling!

It had a fault with a cracked alternator fuse, the one that sits above the battery, which caused some odd issues but now its running pretty well until yesterday...

I've now got a EML light on, VCDS says code P0130 B1S1

I'm guessing that this is the pre cat sensor? I had a quick look but couldn't see it, is it accessible from the engine bay or underneath?

Also, does anyone know if the pre cat sensor is the same as the post cat sensor, are they interchangeable?

It's only a second car so only goes out twice a week so I didn't want anything too fancy but it's a nice drive and I think being 18 years old it still looks pretty good.

Any help would be much appreciated !