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.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: easy
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Common causes
Ordered by how often each turns out to be the cause.
- Sensor element driftedCommon
Parts involved
- Brake Booster Pressure Sensor
P0556 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.