A side diffuser for a vehicle front surface structure, the vehicle front surface structure, and a method for assembling such a structure. The side diffuser guides air entering through air inlets from bumpers of the vehicle to heat exchangers located in front of the engine. The diffuser includes a plate, the back edge of which supports the heat exchangers and the front edge of which supports the bumpers and includes a recess capable of receiving the front crosspiece end of the vehicle. The back side of the diffuser includes: a pivoting axis capable of engaging with a corresponding receiving part provided on the heat exchangers, and an attaching part capable of engaging with a corresponding attaching part provided on the heat exchangers after one rotation of the side diffuser around pivoting axis.