When I had a similar problem on my 2000 (W) Corsa, the orange e/m warning light (consult dealer) having come on, the dealers dignostic computer could only narrow the fault down to one of two sensors. At the time, about 5 years ago, the sensors were about �70 each. I didn`t fancy gambling on tossing a coin & buying one, only to find it was the other at fault. So the mechanic/technician agreed to try one & see if it was ok. Fortunately it was, but I still got a bill for �150 (back then). Sounds like they`re hedging their bets. Try & get them to agree to only replace the faulty item or consult another dealer.