Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0559 Brake Booster Pressure Sensor Circuit Intermittent

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

The brake booster pressure sensor (5 V reference, signal, ground) measures the vacuum in the brake booster. On direct-injection, turbo, stop-start and hybrid engines intake vacuum is scarce, so the engine module watches it and creates vacuum when needed – closing the throttle, suppressing engine stop or running an electric vacuum pump. That makes it an input to idle and throttle control. P0559 means the signal jumps briefly – a loose contact or broken wire under movement – without staying out of range long enough for P0557 or P0558. No manufacturer document available to us uses it; GM catches dropouts through the sample counters of P0557/P0558. CARB requires input components to be checked for circuit faults.

Likely causes

Loose contact at the sensor connector (pin tension, corrosion)
Broken or chafed wire moving with the engine
Sensor with internal dropouts

Symptoms

  • Warning comes and goes
  • Stop-start inactive at times
  • Check engine light (depending on the maker)

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–250
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake booster pressure sensorsensor wiringengine control module

Related codes

P0555P0556P0557P0558

References: law.cornell.edu, gsi.ext.gm.com.