Help in Vectra B 2.0 dt 100 hp

Someone can give me a cable, I am out of Spain curing my Opel Vectra B 2.0 dt 100 hp, good at first the fault light has been turned on and the RPM No VAT account, already lost a lot of force. It seemed an atmospheric die with 20 hp.
The fact is that after cooling I have started it and marches perfectly but when it reaches the normal gear temperature it happens again. I have been investigating several forums and the safest thing is the crankshaft revolution sensor.
Someone can give me a hand and tell me where the happy sensor is located and take the steps to Sur for replacement. I would thank you very much since as I have commented I am in France and the workshops are expensive and also the problems is how to explain it to the mechanic since I am not very good with the language.