On April 18, 2018, the Office of Defects Investigation (ODI) opened Engineering Analysis (EA) 18-002 to investigate reports of braking concerns in model year (MY) 2006-12 Ford Fusion and Lincoln MKZ, and MY 2006-11 Mercury Milan vehicles manufactured with Continental Automotive System?s ABS hydraulic control units (HCUs). Complainants report that after an ABS braking event (initiated by slippery or uneven surfaces) the brake pedal moved towards the floor and the vehicle stopping distance increased beyond driver expectations.Inside the HCU are four hydraulic normally closed (NC) valves with zinc-coated moving armatures that control the flow of brake fluid. Unstable brake fluid can degrade over time, allow the brake fluid to gel, and corrosion to form on the armatures. The high-viscosity gelation and corrosion can cause the armatures to become stuck (open). In some cases, braking returns to normal when the armature(s) subsequently become unstuck. The intermittent condition proves difficult to diagnose with complainants reporting having (non-HCU) repairs conducted only to have the condition return.During the investigation, 14 HCUs from complaint vehicles were recovered, including seven from reported crashes. NHTSA?s Vehicle Research and Test Center (VRTC) disassembled the HCUs, removed the four NC valves in each, and confirmed 22 of the 56 NC valves contained stuck armatures. On seven of the 14 HCUs, both front wheel armatures were stuck, on nine of the 14 HCUs two or three armatures were stuck. And 52 of the 56 NC armatures exhibited corrosion of the zinc coating. Forces required to extract stuck armatures from the valve sleeve were measured to range from 1.1 to 18.0 lbs. VRTC also conducted ABS braking tests on a variety of test surfaces that showed HCU failures cause increases in pedal travel and braking distances. Testing also showed that if the driver was able to apply four times the brake pedal force and two times the brake pedal travel, then high-vehicle deceler