Vacuum leak in the brake servo hose, non-return valve or hose connections; Faulty or worn mechanical or electric vacuum pump (where fitted); Faulty brake vacuum sensor or its wiring and connector; Leaking or split brake servo diaphragm; Engine-related low manifold vacuum, such as an intake leak or fault in the air control system; Blocked or collapsed vacuum line or pump relay or supply fault (electric pump systems); Control unit fault or outdated software, where the manufacturer has identified it as a known cause.

P050F

Brake Assist Vacuum Too Low.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
5: AreaVehicle speed, idle control and auxiliary inputs
0F: FaultThe specific fault in that area

What it means

P050F is the generic code for Brake Assist Vacuum Too Low. The control unit has seen the vacuum available to the brake servo (booster) fall below the level it expects, usually from a vacuum sensor or pressure reading, so power assistance to the brakes may be reduced. It is mainly seen on engines that cannot rely on strong intake vacuum, such as direct injection petrol, turbocharged and some hybrid or start-stop vehicles, where a vacuum pump or other source is used.

Symptoms

Hard or stiff brake pedal needing extra effort
Longer stopping distances than normal
Brake warning light or engine warning light on
Hissing noise from the pedal area or engine bay when braking
Rough idle or high idle if there is a vacuum leak
Start-stop system not working or engine not stopping at rest

Possible causes

Vacuum leak in the brake servo hose, non-return valve or hose connectionslikely
Faulty or worn mechanical or electric vacuum pump (where fitted)likely
Faulty brake vacuum sensor or its wiring and connectorpossible
Leaking or split brake servo diaphragmpossible
Engine-related low manifold vacuum, such as an intake leak or fault in the air control systempossible
Blocked or collapsed vacuum line or pump relay or supply fault (electric pump systems)rare
Control unit fault or outdated software, where the manufacturer has identified it as a known causerare

How to diagnose

Read all stored codes and freeze frame data, noting engine speed, load and conditions when the fault set, and check for related vacuum, MAP or brake codes
Check the brake pedal feel with the engine off, then start the engine and see whether the pedal sinks and firms up as it should
Inspect the servo vacuum hose, fittings and non-return valve for cracks, splits, loose clips and oil contamination
Listen for hissing at the servo and engine bay with the engine running, and check for intake leaks
Check the vacuum sensor connector and wiring for damage, corrosion and poor contact, and compare its live reading with expected values
Test the non-return valve to make sure it passes air in one direction only
Test vacuum at the servo with a suitable gauge and check vacuum pump operation, including supply, relay and fuses on electric types
Follow the manufacturer's procedure for the specific model, as the vacuum source and test method vary by engine and vehicle

How to fix

Replace split, perished or loose vacuum hoses and fittings
Replace a faulty non-return valve
Repair or replace a failing vacuum pump or its relay and wiring
Replace a faulty brake vacuum sensor, or repair its wiring or connector
Replace the brake servo if the diaphragm is leaking
Repair any intake or engine vacuum leak, and apply a manufacturer software update only if a known fault calls for it

Can I keep driving?

High severity

Avoid driving until the brakes have been checked, as loss of servo assistance means a much heavier pedal and longer stopping distances. If it must be moved, go only a short distance very carefully, leaving large gaps, or have the car recovered.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.