Atmospheric pressure sensor (539): Location:

4-cyl petrol:  on the engine's top left front corner by the camshaft cover

Fig 1: Identifying Atmospheric Pressure Sensor (539) 4-Cyl Petrol

Courtesy of SAAB-SCANIA OF AMERICA, INC.

4-cyl diesel:  under the glow plug control module on the battery's radiation protection

Fig 2: Identifying Atmospheric Pressure Sensor (539) 4-Cyl Diesel

Courtesy of SAAB-SCANIA OF AMERICA, INC.