How do I determine if vacuum leak is in system or bad pump on 2003 Ford Taurus

engine light stays on, does not flash. The code is for vacuum system failure. Not sure if it is in hoses or in vacuum pump. How do I determine ? Car runs well, heater/air conditioner runs well. Short of expensive trip to dealership I could use some ideas

Asked by for the 2003 Ford Taurus
Do you mean Evaporative Emissions system issues - like P0455 P0456 P0457,that sort of thing?
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I could be as simple a your gas cap not sealing also. Put some vasoline on it and make sure it's tight.