possible causes? O2 sensor low voltage ie running lean!

[dr.gonzo]

Not realy a golf, its wor lass's beetle but its an AQY 2litre engine same as the mk4gti only the rest of it looks stupid
anywho, im getting low voltage errors at bank1 o2sensor!
the sensor is brand new so i was wondering what other possible faults could be causing this?
im thinking maf?or vaccuum leek or something? id assume id get a fault code for a vacuumleak pinpointing it tho or a maf error?
thing is the sensor was solid and threads were stripped so i couldnt get it out so i had to remove the whole intake system and manifold to extract it and recut the threads before putting it all back.
is it possible i need to clean the throttle body? could this trigger a low voltage?
ok now im gona get slatered here!
errrrrrrrrrrr its a cheap sensor and i had to extend it to make it reach so it has 2 joins(soldered tho) in it aswel.
im going to get a proper vw one  but i was just curious of other things to check before i do?
cheers!

[Rhyso]

if you're getting low voltage errors have you checked the wiring going into the O2 sensor

sadly a lot of people replace the sensor thinking its the problem but 7/10 its the actual wiring that has broken down

[dr.gonzo]

yeah seems ok but im gona clean all the contacts to be sure.
one of the first things i done was go over the wiring.
well i say one of the first things, wot i mean is i forgot to plug the  ecu wiring back in and got a sh!t load of error codes and the car was like a bag o hammers, being out of sight i hadnt realised so was tearing me hair out wondering what the hell was wrong.
im not sure but its ringing a bell that i got a no activity code at one point which points right at the wiring but im not 100% as id erased the code before i checked the book and couldnt for sure remember what it was for definate.
im hoping i get that code again, then i know for sure its the wiring somewhere.
cheers

[dr.gonzo]

i think ive sussed it!
ive put in a zirconia but i think it needs planar sensor!!!!!
makes sense cos the light comes on within 2 mins of being cold BUT if the car is warmed thoroughly it seems to stay off untill its stood a while, then back on again from cold!