15 where is the intake pressure sensor of the three-cylinder Mercedes Smart?

One is upstream of the throttle valve and the other is downstream.

Manifold absolute pressure sensor (MAP). It is connected to the intake manifold through a vacuum tube. With the different engine speed load, it senses the change of vacuum degree in the intake manifold, and then converts the change of sensor internal resistance into a voltage signal for ECU to correct the fuel injection quantity and ignition timing angle.