P2D51Air Assisted Injector Control Circuit

How the car detects it: P2D51 is the general electrical code for the control circuit of an air-assist injection system, the circuit counterpart to P0065 to P0067. Assist air flowing around the injector tip breaks the fuel spray into finer droplets. In Ford's patented layout the air bypasses the throttle and is metered by a solenoid valve that the engine computer drives with a pulse-width signal, so a circuit fault concerns this valve, its wiring or the driver stage. Another Ford patent shows a passive variant in which only a shroud on the injector meters the air and nothing electrical can fail. No manufacturer documents P2D51 publicly. Without the valve, atomisation suffers mainly at idle and in cold starts. Low and high: P0066, P0067. Air-assisted DEF dosing uses separate reductant codes such as P2059.
What you may notice: MIL on
Unsteady idle or harder cold starts
Slightly higher hydrocarbon emissions
Likely causes: LikelyOpen or shorted coil in the air-assist solenoid valve
PossibleDamaged wiring or corroded connector at the valve
RareFaulty output stage in the engine control module
Inspection (ITP): Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
Repair: Medium · Often possible to do yourself.Typical cost: €40 – €250
Related codes: P0065
P0066
P0067

Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.