If it's a hard fault the diagnostics would pick it up in milli-seconds, an intermittant fault might take an engine run or a drive with the diagnostics connected either way it should'nt be more than 1 hr if it takes longer the person does'nt know what he/she is doing, when you say "crankcase sensor" I would take a guess that you mean "crankshaft sensor" or even "camshaft sensor" either way you can quickly select the diagnostics to look at the named sensor and very quickly you would see if it is putting out the correct signals,
Suggest you try another garage!!!!
nigel
March 2009