OBD-II code · Powertrain (generic)
P0556 Brake Booster Pressure Sensor Circuit Range or Performance
Same as P0555 with the signal in plausible range yet not matching the engine model - drift, partial blockage of the reference port.
Is it safe to drive with P0556?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySensor element drifted
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.4–1.4 h
- Emissions test
- Usually unaffected
- Parts involved
- Brake Booster Pressure Sensor
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.