BK2Q-9K546-AG — Symptoms & Failure Modes
Common symptoms and verified failure modes of a failing Siemens VDO BK2Q-9K546-AG (A2C59517051 / 5WS40745) Ford 2.2 TDCi Puma Piezo Injector.
Hard starting / extended cranking · high
A leaking piezo injector with high spill return drops rail pressure during cranking so the engine struggles to fire.
Rough running, knocking or rattling · high
An out-of-balance injector under/over-fuels its cylinder, producing a knock or diesel rattle.
Limp mode / loss of power · high
Rail-pressure or injector-control faults trigger an ECU derate to protect the fuel system.
Low fuel rail pressure / pressure-regulation codes · medium
Excessive injector spill (back-leakage) prevents the system holding target rail pressure.
Black or white smoke · medium
Poor atomisation from a worn or coked nozzle.
Increased fuel consumption / misfire on one cylinder · medium
A single failing injector raises consumption and produces a cylinder-specific stumble.