Hi, I got a vectra c estate on an 07 plate fitted with the vvti engine, I only owned the car since may 2011 and have had the eml light come on 4 times, It seems to come on every time I go on the motorway. Lucky enough when I bought the car I took out an extended warranty. Each time the eml light has come on I have sent it to my local Vauxhall dealer

First time - fault code was po420 , they changed the oxygen sensor
Second time - Same fault code as above, so they changed the ecu unit and also said it could be a suspect cat,
Third time - same fault code again so replaced oxygen sensor again

eml light is now back on and have read the fault myself with an after market code reader,
What I am asking is if anyone has experienced the same problem and does it sound like I need a new cat, as dont want to spend any money on a new cat unless I have to as the warranty will not cover the cat.

Thanks for your help