Brake Booster Vacuum Sensor
WARNING: This page is about a different car, the 2013 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The brake booster vacuum sensor is a piezoelectric device used by the ABS module to monitor the vacuum in the brake booster. The sensor is hardwired to the ABS module by 3 circuits. One circuit is for the 5 volt sensor supply, one circuit is for sensor ground and one circuit is for sensor output. The sensor output ranges from 0.7 volt to 4.9 volts, depending on the amount of vacuum in the booster. The sensor is located on the front of the brake booster at the 6 o'clock position and can be serviced separately from the brake booster.