16600-5X30A — Symptoms & Failure Modes
Common symptoms and verified failure modes of a failing Denso 16600-5X30A 2.5 dCi (YD25DDTi) Common Rail Injector.
Hard starting / extended cranking · high
Injector back-leakage drops cranking rail pressure on the YD25, making the engine slow to start, especially cold.
Rough idle and vibration · high
A worn or leaking injector unbalances cylinder fuelling, producing a shaky idle on the 2.5 dCi.
Black smoke · medium
Poor atomisation from a worn nozzle over-fuels the cylinder.
Loss of power / limp mode · medium
Out-of-range injector delivery triggers reduced performance or limp mode on the YD25DDTi.
Knocking / diesel rattle · medium
A leaking injector causes a pronounced top-end knock on the YD25, often mistaken for timing-chain noise.
Increased fuel consumption · medium
Over-fuelling or internal leakage wastes fuel and can fail emissions.