Powertrain, generic · Vehicle speed, idle control and auxiliary inputs
P050F Brake Assist Vacuum Too Low
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
GM (from about model year 2017/18) monitors the brake booster with a vacuum sensor: with the pedal at rest and high intake vacuum the booster must hold its vacuum; a loss over time is filtered as a drift ratio, and above a threshold P050F sets, MIL after two trips. It runs with the engine on, during start-stop auto-stops and after switch-off. Without enough brake vacuum the module must throttle, restart the engine from auto-stop or request a pump – which affects idle and start-stop – and brake assistance can drop. Ford and FCA do not use P050F.
Likely causes
Leaking vacuum hose or check valve
Leaking diaphragm in the brake booster
Vacuum sensor or its seal faulty
Electric or mechanical vacuum pump weak (where fitted)
Symptoms
- Check engine light on
- Hard brake pedal, especially after auto-stop
- Hissing at the pedal, start-stop stops less often
Repair estimate
DifficultyMediumDIY possible
Parts and labour€20–600
Time0.5–3 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
brake boosterbrake booster vacuum sensorvacuum hoseengine control module
Related codes
References: gsi.ext.gm.com, gsi.ext.gm.com, en.wikipedia.org.