Powertrain, generic (extended)

P2D51 Air Assisted Injector Control Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Open or shorted coil in the air-assist solenoid valve
Damaged wiring or corroded connector at the valve
Faulty output stage in the engine control module

Symptoms

  • MIL on
  • Unsteady idle or harder cold starts
  • Slightly higher hydrocarbon emissions

Repair estimate

DifficultyMediumDIY possible
Parts and labour€40–250
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

air assisted injector solenoidwiring harnessecm

Related codes

P0065P0066P0067

References: patents.google.com, patents.google.com, law.cornell.edu.