Ok...doesn't really answer the question though - have you replaced lambda sensors in the absence of error codes, and seen a benefit? While they have 't failed, I'd asume they're like many electrical components which can suffer from reduced performance without necessarily triggering a noticeable issue - especially when it happens over a large period of time - eg dirty mafs, old coil packs etc. Might not cause the car to drive badly - but may hinder full potential, or affect fuel economy compared to another car with new O2 sensors.

Interested to hear whether anyone's changed the parts as per bmw and bosch recommended interval and seen a benefit.

Many thanks!