I had a Mark 4 V5 and this light came on 5 times, twice it was coil packs and the engine ran really badly in "safe" mode and had to be recovered, twice it was just sensors but once it was because the engine fan fuse had blown!! If your engine is running ok which it sounds like it is then I would guess either a sensor (cost about £100 to get fixed) or if you are lucky the fuse (15p)
Hope this helps