I have a 1997 S70 2.5 20v. The lamda sensor warning light has come on three times over the last 12 months and been reset by volvo twice. Volvo say there is no fault but charge me £22 to reset it each time. I have noticed that each time the warning light comes on the road has been wet but other than that I can find nothing wrong with the wiring etc. (the Volvo dealer tells me that it is the rear lamda sensor which is throwing up the fault). Any ideas?