P306d Peugeot - //free\\

The success of the Peugeot 306 diesel was largely due to the legendary PSA XUD engine series, and later, the DW10 HDi engines. 1.1. The 1.9L XUD9 (Non-Turbo and Turbo)

In simple terms, the engine is pulling in either more or less air than the throttle plate position says it should. Because the data from these two components conflicts, the ECU triggers the Check Engine Light (CEL) because it can no longer guarantee optimal combustion or emissions control. Technical Overview: Affected Peugeot Vehicles

In simpler terms, the ECU expects a very specific amount of air pressure inside the engine intake for any given throttle valve position. If the detected manifold absolute pressure (MAP) is too high or drastically unaligned with where the throttle blade is physically open, the ECU flags the P306D code to protect the engine from a compromised air-fuel ratio. ⚠️ Common Symptoms of Fault Code P306D

This means the engine computer (ECU) is comparing two pieces of data—the predicted air pressure calculated from the throttle position and the actual measured pressure from the MAP sensor—and they do not match.

A very common cause, particularly on 1.6 PureTech engines, is the valve that controls the EVAP purge. If this valve leaks or sticks open, it introduces extra, unmetered air into the intake manifold, messing with the coherence check.