Hi Guys
Since buying the VX (2 weeks ago) I have had the Check Engine light on, it was on when I bought it and the old owner said it had been on a few days and his local garage told him it was a broken Cat Converter. I wasn't worried about that because it is LPG converted (here in the UK) it doesn't need one to pass the yearly safety test (MOT).
I have got my hands on a fault code reader now and it shows the fault as
"P0131 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)"
Does this code show a Cat Fault or a Lambda Sensor fault?
If it is a Lambda Sensor fault then how do I know which one it is? and where do I get one from? I cant find them listed in the UK anywhere
I have cleared the code a few times but it returns after about 10 mins of driving.

Any ideas or pointers
Cheers