P0557 code meaning
Brake Booster Pressure Sensor Circuit Low
Powertrain system Generic code P05xx codes Check engine light
What P0557 means
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.
P0557 at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P0557
- Check engine light or brake booster warning
- Stop-start inactive
- Often no change in driving
Common causes of P0557
- Most likelySignal line open or shorted to ground, connector loose or corroded
- Possible5 V reference open or shorted to ground
- PossibleSensor faulty internally
- Less likelyEngine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake booster pressure sensorSensor wiringEngine control module
What each part of P0557 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 57 | The exact fault in that area. |
What to do next
- Note P0557 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0557
What does P0557 mean?
P0557 means "Brake Booster Pressure Sensor Circuit Low". The brake booster pressure sensor (5 V reference, signal, ground) measures the vacuum in the brake booster. It is a generic code, so it means the same on every make.
Is it safe to drive with P0557?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0557 fail an emissions test?
P0557 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0557 to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0557 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.