Issue With Service Nh03 - Fuel Up And Then Run Light Engine To Manchester Victoria....

I selected the Class 40 to do a service and I picked NH03 - Fuel up and then run light engine to Manchester Victoria to pick up the waiting newspaper train in platform 11. One of the tasks is to re-fuel the locomotive except when you get to the refueling station the scenario dose not make you do this, you simply stop at the marker and move to the final part. I never got a chance to re-fuel a class 40 yet so I thought this scenario would give me that chance.

 

What stops you from just jumping out and refueling it when you are there?