— Ford soft brake pedal problems caused at least 26 crashes and three injuries, but a formal investigation has been closed after Ford recalled more than 600,000 vehicles.
The National Highway Traffic Safety Administration (NHTSA) opened the investigation in 2016 after owners complained about soft brake pedals and problems getting the vehicles to stop.
The investigation was upgraded in 2018 to include more than 1 million model year 2006-2012 Ford Fusion, 2006-2012 Lincoln MKZ and 2006-2011 Mercury Milan vehicles that suffered from soft brake pedals due to the anti-lock braking system (ABS) hydraulic control units.
Vehicle owners said the soft brake pedal problems occurred after activation of the anti-lock braking systems when driving on slippery or uneven surfaces.
The anti-lock braking hydraulic control unit has four valves with moving armatures coated with zinc that control the flow of brake fluid. Those valves are normally closed, but they can stick open because brake fluid can degrade, turn into gel and corrode the armatures.
NHTSA says the soft brake pedal problem was difficult to diagnose because the valves can become unstuck and allow the brake pedals to function normally.
In one test, NHTSA collected 14 ABS hydraulic control units, seven of them from vehicles that crashed. The control units were disassembled and investigators confirmed several with valves stuck open.
Corrosion of the armatures was seen and NHTSA confirmed the wheels could still lock even though drivers noticed soft brake pedals.
The brake fluid used for the vehicles was a specific formulation of DOT 3 fluid provided by CCI Corporation between February 2006 and July 2009, and it differed from the brake fluid used in other Ford vehicles.
The Ford soft brake pedal recall issued in 2019 saw dealerships test the hydraulic control units and replace them if they failed the test. The new units have black oxide armature coating that showed no problems with corrosion. In addition, all dealers replaced the DOT 3 brake fluid with an improved DOT 4 fluid.
NHTSA believes the problems may be solved and closed the investigation based on Ford's soft brake pedal hydraulic control unit recall of 2006-2010 Ford Fusion, Mercury Milan, Lincoln Zephyr and Lincoln MKZ vehicles.