Don't know what it does, but VAG said the same as "Supercharged" above (it is required). The sensor isn't actually considered part of the ht lead system. The only one I could get from VAG was a sealed unit (the same as already fitted), and I was told that I would need to take the end of the ht lead to pass it thru the sensor. Easy enough job with VAG leads as they are designed with this in mind, not so easy with the blue igniters that I have bought. Car is booked in for a diagnostic on 21/07, hopefully will find out what to do then.