I've just changed the pre-cat O2 Sensor (Lamda) on my non-S R56 Mini Cooper 2008. The sensor had done 67,000 miles and early symptoms of failure, before the engine light came on, was that the car would run rough or even stall during weather below 10 degrees C. Normal engine codes for the pre-cat sensor were displayed.
A new Bosch 02 sensor from GSF Car Parts was £118+ VAT. I also picked up the Laser 22mm deep socket with a cut out to make the job easier - £11.
The images in the Haynes manual were poor. The image below shows the exhaust heat shield removed - 3x 10mm bolts on top and 3x 10mm bolts along the front (used a ring and open ended spanner to get off).
Once the shield is off you can see the sensor at the top - i have used a red arrow to show where it was after I had taken mine out. The sensor's connector was a bit fiddly and I took its mounting off of the oil filter housing to make it easier - single 10mm bolt.
This is the deep socket with the cut out and the original sensor in it.
The whole job took me 80 minutes and that included resetting the engine light with my OBDII scanner. The car now runs soooo much better...:big_grin: