Visual Inspection and Diagnostic Pre-checks

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.

Inspect the brake booster for vacuum leaks.
Inspect the brake booster for any obvious signs of damage.
Inspect the brake booster vacuum sensor harness and connector of any obvious signs of damage.
Make sure the brake booster vacuum sensor electrical connector is free from any corrosion or other contaminants.