Kühlmittelstand im Ladeluftkühlkreis zu niedrig

On engines with a water-cooled charge air cooler, a low level in that circuit specifically — which is separate from the engine's own cooling system and often has its own header tank. That separateness is the whole point of the entry: an engine coolant level that reads correct says nothing about this circuit, and the tank for it is easy to miss.

Low level shows as charge air temperature rather than engine temperature. The cooler cannot reject heat, intake temperature climbs under boost, and the module pulls timing or limits boost to protect the engine — so the complaint is a power loss that appears after sustained load and recovers after a rest. The engine temperature gauge sits exactly where it always does throughout, which is what makes the fault confusing.

These circuits are low-volume, so a small loss matters and air trapped in one stops circulation entirely. Find the leak rather than topping up, and bleed the circuit by the correct procedure afterwards — an air lock in a low-temperature circuit will reproduce every symptom of a low level with the tank full.