Oxegen sensor.

[Mark@Elite]

Hi, just wondered if anyone could help with a problem I've got.
I have just bought a 2002 2.2 Vectra Elite, with 90 thou on the clock.
When i bought it it had the emissions light on, i put it straight into my local mechanic who is a ex vauxhall mechanic. He plug in his diagnostic machine and it came up faulty oxygen sensor. He reset it and said try it now and if the light comes back on we will have to change the sensor.
On the trip home the light stayed of but when i went out later on in the day it came back on again, so i booked it in to have the sensor replaced.
Once more he plugged the diagnostic machine in and it said oxygen sensor fault, he changed the sensor and said all was fine.
I drove home and all was well, but once again when a started car up again the light stayed on.
Anyone have any ideas on why it might be doing this so i can give some info to my mechanic?

Many thanks, Mark..

[Gsi3.2]

has he done an emissions test to see if the post cat lamda is running fine as well as the precat one??? also, what lamda values is he getting?

[Mark@Elite]

I have absolutely no idea m8, its back in on Tuesday for a look, but ill ask him to check what you said.

Mark..