Chassis, generic

C0566 Brake Booster Solenoid Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Some vacuum brake boosters carry an electrically operated valve that lets air into the working chamber without pedal input – for emergency brake assist or, on hybrids, to blend friction and regenerative braking. An Aisin patent shows the idea: when energised, the solenoid admits atmospheric pressure to an auxiliary chamber and raises boost. C0566 reports an open circuit in this solenoid's wiring or coil. Ford's 2015–2019 hybrids store the ABS fault C0022 (brake booster solenoid) and mirror it as C0566 in the hybrid powertrain module; while it is active, Ford's pump motor and valve tests are suspended. Normal pedal boost usually remains, but automatic brake assist and smooth blending are lost.

Likely causes

Solenoid connector loose, unlatched or corroded at the booster
Broken wire between ABS module and booster solenoid
Open solenoid coil inside the booster

Symptoms

  • Brake system or stability warning
  • Brake assist or regenerative blending unavailable
  • Pedal feel changes on hybrids

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€40–900
Time0.5–3 h

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

Parts involved

brake booster solenoid

Related codes

C0567C0568C0569C0022

References: fordservicecontent.com, patents.google.com.