V70 Atmospheric Presure sensor

[mzjfb7]

I have a UK V70 AWD (1997). and the Engine Mngt Light ('Alpha' symbol) used to come on continously and go off again after a few days . I took it into a Volvo dealer, and they reset it and said it was the Atmospheric Presure sensor, and to see how it goes it might be faulty. anyway it is coming back on and off again, and i'd like to know where it is so I can check it out. Does anyone know?

TIA
Matthew, UK