I'm certain about B1S1. I looked under the hood this AM. You are correct --- it is clearly visible and reachable w/o removing the engine plastic cover. However, to remove the O2 sensor wire plug/harness, it appears to be further towards the rear of the engine. I could not see where the wires ended. So, looks like I need to remove the engine cover.
Originally Posted by Efthreeoh
You must be talking about the B1 S2 O2 sensor then. The Bank 1 Sensor 1 is the O2 sensor in the top of the front exhaust manifold (cylinders 1, 2, 3) that you can easily see on the right side of the engine. This this for an N52 of course, which is the engine in your car. I have both types of sockets (off set and deepwell-split). Either should work.
I did my sensor just after the time Eninty posted the DIY and the price for the OEM sensor (B2 S1) was $55 from Tischer.