Lotus Elise k series help

[Callum]

Having issues with my 2001 k series elise. 
First of all I had a engine light on the dash with a P0420 code fault I was told this indicated the downstream lambda sensor so took this off and cleaned and it worked for a while. Then came back up so decided to change the sensor, now I am getting both a P0420 and a P0141 fault code as well. I tried changing the sensor back but this is still the same, wondering if anyone could help what it could be, is the voltage sent from a fuse somewhere? 
Any help would be appreciated. 

[Kevin Wheeler]

Not sure if this will help, but I had a problem with overfuelling, I think it was. I had several lambda sensors changed by the local garage which did not fix the issue. I then took it to my Lotus specialist who said "oh yeah, that is a broken wire. Just had another one of those in".

Replaced the broken bit and it was all sorted. I might suggest getting the wiring checked if you can.

Mine is an '03 K series Elise. 130K miles now.

[Techyd]

I had the same on mine just over a year ago, turns out both sensors had essentially failed!  I would recommend changing them both 🙂