Do you mean the Lambda at the top? Then yes you need it.
If you mean the o2 sensor thats down the bottom then no you dont.
Yeah lamba mate... Can get my one off my old decat
They can be a complete bastard to get out, i have one here if you dont get it.
How much Ian need it for sat mate
Ill make sure i can get it out the CAT first, it was brand new from Toyota and only used for a month while we waited for our WEPR kit to arrive.
if you soak it in wd340 or simialar over night and get a good 22mm ring spanner it should come, may need some persuasion with a hammer on the spanner to shock it though