I had a quick look on-line, it appears both pins 2 & 4 need to each be connected to a separate Analogue Input pin. The reading from both pins needs to be compared.
Extracted from the data sheet..
"The output voltage of the differential or gauge sensor
increases with increasing pressure applied to the pressure
side (P1) relative to the vacuum side (P2). Similarly, output
voltage increases as increasing vacuum is applied to the
vacuum side (P2) relative to the pressure side (P1)."