O2 sensors on Newage STI
 

I have a re-mapped Eu STI 2003

Constant Motorway driving causes an O2 error CEL.

Car's O2 settings are set to maximum by highly regarded mapper, but also
Delta Dash highlighted an O2 rear bank sensor error (=0).

Had car sent to dealers:

Dealer says there is no rear bank sensor on Eu STI, only on JDM STI, so had(front) O2 sensor replaced under warranty,

BUT

light still comes on...

Anyone have any ideas?

Obviously the dealer misunderstood and your rear O2 sensor has problem, connection error etc

did raise the question that it was the rear sensor that needed replacing.

They checked, and said there is only one sensor on the Eu cars, so it had to be the front...