P0557: Brake Booster Pressure Sensor Circuit Low

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.

Medium severity. Can I keep driving?Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

Check the hoses, clamps, and intercooler
With the connector unplugged, check whether the signal wire is making contact with ground.
Compare commanded and actual pressure in live data
Check the actuator's movement
Check the vacuum hoses and the solenoid valve
Check the oil and the turbo shaft play before replacing it

Good to know

Repair difficulty: medium

What each character of P0557 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
5: Speed and idle
57: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0557?

Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.

What causes code P0557?

The most common causes are: signal line open or shorted to ground, connector loose or corroded; 5 V reference open or shorted to ground; sensor faulty internally.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.