If you are comfortable working under the hood, you can start by checking the or cleaning the MAP sensor . However, because this code is a "coherence" error, it can sometimes be a "ghost" caused by a weak battery or software glitches.
"Coherence between the position of the motorized throttle-housing (air mixer) and the inlet air pressure" p306d peugeot fixed
This is the #1 solution for P306D when contamination is suspected. If you are comfortable working under the hood,