Fault Codes Poo31

[Riots Scooby]

Hi

I am new to this site and hoped someone could help me shed some light on a fault code I have had come up on a diagnostic machine, for my 2001 Subaru WRX wagon....

Code is POO31 (wire fault,HO2S, EMC fault)

My mechanic has checked wiring all seems ok....

Have just had the Lambda sensor changed at £250 for the part from Subaru !!!

What else could it be...he was hoping that the light would go out on dashboard...but it hasnt.....recheked on Diagnostic and same fault code has come up....ARGHHHH!!!!

I am in Slough can anyone offer me advise or help me get rid of this problem....as am worried about it being driven round (by the wife)

I am hoping its not a ECU/EMC fault as I've been told thats a pricey fix....SGT have said its highly unlikely....

Please help me

Thanks

RIOT