Niederdruck-Kraftstoffsensor defekt

The sensor watching the lift side of a high pressure fuel system — the transfer pump's feed to the high pressure pump — rather than the rail itself. The whole reason it exists is to let the control module tell two very different faults apart: a rail that cannot reach pressure because the high pressure pump is failing, and one that cannot reach pressure because nothing is being delivered to it. Without this sensor both look identical at the rail.

So a fault here costs more than one reading. With the low pressure signal untrustworthy the module loses its ability to attribute a rail pressure shortfall, and it will often store rail codes alongside this one. Read the low pressure sensor's own status first — diagnosing the rail while its supply reading is unreliable is how a perfectly good high pressure pump gets replaced.

The failures are ordinary. Corrosion in a connector sited under the vehicle near the tank, a chafed harness where the loom passes a body seam, water sitting in the plug after a wash, or a genuinely drifted element. A reading that is plausible but wrong is the dangerous one, because it survives every circuit check — compare it against a mechanical gauge rather than against expectation.