I've got a '04 S60 2.5T with 160k and recently I've been getting that "Reduced Engine Performance" message followed by absolutely no power when pressing the accelerator. The codes have been P2108 (ETA) twice and P2135 and P0221 (Accelerator pedal) twice. My question is, which one is it?? How should I go about troubleshooting this?

Iv'e looked at previous posts and they seem to go one way or the other, without any clear distinction.

Many thanks for any input.