My 2008 US spec 997 C4S is now in the UK running on UK 98 oct gas which usually has less than 5% ethanol

Through PWIS we can see DME calculated the lambdas running between 0.98 and 1.02 (3,000 rpm). No error codes, DME thinks its doing a great job.

However from sniffing the tail pipe, the Lambda is reading a constant 1.05 (on both sides) which is out of the UK allowable range of 0.97 to 1.03. (Had this done in 3 different places, all the same result)

We have checked the AWE ehaust system (200 cell CATS) for leaks and are pretty confident that the sysytem is tight

Any info or comment on why the DME lambda is being calculated with a negative offset ?

US cars have a different part number for the upstream O2 sensor from the european cars. Downstream sensors are the same for US and Euro. Could it be that the US upstream O2 sensor is calibrated / optimized for fuel with 10% ethanol . . .?