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

P0557 Brake Booster Pressure Sensor Circuit Low

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. P0557 means the signal voltage is too low: GM 2018 below 5 % of the 5 V reference in 320 of 400 samples (about 5 s), GM 2006 below 0.04 V; type B, two trips. Typical are a signal shorted to ground or an open signal or 5 V line. As low voltage means plenty of vacuum, the module would wrongly assume enough – so it uses a substitute value.

Likely causes

Signal line open or shorted to ground, connector loose or corroded
5 V reference open or shorted to ground
Sensor faulty internally
Engine module

Symptoms

  • Check engine light or brake booster warning
  • Stop-start inactive
  • Often no change in driving

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–250
Time0.5–1.5 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

P0555P0556P0558P0559P0641

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.