Theory Of Operation
WARNING: This page is about a different car, the 2025 Jeep Compass. However, it is still accessible from the selected car via links, so may be relevant.
The Vacuum Pressure Sensor indicates a low vacuum condition in the vacuum booster. After the cold start phase (i.e. 3 min after engine is running) and with engine running above 400 RPM there should be at least -135 mbar (-2.0 psi) of differential pressure in the vacuum-chamber. If the pressure is between 0.0 mbar (0.0 psi) and -134 mbar (-1.9 psi) for more than two minutes at a speed above 3 km/h (7 mph) this fault will set.