2E7C

A forum poster in a 2022 thread gives the layout from the wiring diagrams: the BSD line is on pin 2 of the water pump connector, on pin 1 of the battery sensor and oil condition sensor connectors, and reaches the engine computer on three pins (X60007 pin 26, X60001 pin 3 to the battery sensor, X60005 pin 35 to the alternator), which he believes are connected inside the engine computer. He suggests starting with corrosion on the three engine computer connector pins and a short to ground on any device connector.

That thread's owner, with a 2010 N54 335i, had unplugged each device in turn with 2E7C returning every time; the car idled rough, the oil sensor read inactive and it eventually overheated. His solution post: a European mechanic found corrosion on the engine computer pins and spent a couple of hours cleaning them, and the car was back to normal so far. He had not fitted the white waterproof cover over the engine computer before the car went through a wash.

In a 2024 thread on an E91 325i, all four devices (alternator, water pump, oil sensor and battery sensor) were disconnected and the code returned; the oil level stayed inactive in ISTA while the oil temperature read correctly. The owner found good continuity, no short and no voltage loss on the wiring, then put an oscilloscope on the alternator BSD line and saw a steady 1.1 volts with ignition on, even with the devices unplugged, and concluded the engine computer was next. A later poster there says they read it could be a component inside the engine computer; that is hearsay, and the thread has no outcome.