Whats the difference

[SupraKingz]

I'm trying to figure out what could be the issue with my 1j because it is giving me the code 31 meaning air flow meter and can't figure out how to resolve this code but i've come down to maybe the map sensor but I was wondering whats the difference between the map against the fire wall and the one by the driver side wheel well.

 

[JonoTurbo]

The one on the firewall is the one used by the ECU to determine airflow into the engine. The one by the fender is the sensor for the stock boost gauge.