Symptom hub
Hard Brake Pedal: Brake Booster, Vacuum Leak, or Pressure-Sensor Clues?
A brake pedal that suddenly feels hard changes the whole priority order. That pattern pushes brake-booster vacuum supply, booster integrity, check-valve function, and booster-pressure sensing ahead of generic reduced-power thinking.
Likely related codes
Start your diagnostic path here
P0171 — System Too Lean (Bank 1) P0174 — System Too Lean (Bank 2) P0507 — Idle Control System RPM Higher Than Expected P0068 — MAP/MAF - Throttle Position Correlation P2279 — Intake Air System Leak P051B — Crankcase Pressure Sensor Circuit Range/Performance P0556 — Brake Booster Pressure Sensor Circuit Range/Performance P0557 — Brake Booster Pressure Sensor Circuit Low P0069 — Manifold Absolute Pressure - Barometric Pressure Correlation P0558 — Brake Booster Pressure Sensor Circuit High P0559 — Brake Booster Pressure Sensor Circuit Intermittent