Which O2 sensor is this?

[Dan MR2]

Hi, which O2 sensor is this fault code, P0142 S2 B1
I've looked at some diagrams and it looks like the one on the cat?
On the diagnostic equipment the other two sensors had some readings around 0.800 when it was being tested, the faulty one had reading around 0.010 at the same time.
The diagnostic bloke thinks the sensor might still be working, just could be a poor connection or corroded wire?

[Carolyn]

You're correct.  The one on the main cat.  Same as the others but with longer wire.  Almost certainly faulty.  You could try some contact cleaner spray inside the connectors...

[Dan MR2]

Ok thanks for the reply.

[BahnStormer]

Don't despair - worst case, it's £25 for a ropey replacement or £50 for an OEM spec one that will last...