Brake Booster Pressure Sensor Circuit Range/Performance
What it means
P0556 means the brake booster pressure sensor is reporting a value that is out of its expected range or responding erratically. The sensor tells the ECM how much vacuum or pressure assist the booster has, so a faulty reading can affect how the brake pedal feels. It is most often the sensor or its wiring, but a failing booster can also set it.
Can I keep driving? Drive with caution — the brakes still work mechanically, but the pedal may feel hard or inconsistent, so have it checked promptly.
Real-world scan data
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
Common symptoms
What you'll notice
- Check-engine light on
- Hard brake pedal or inconsistent pedal feel
- Reduced braking assist / effort feels higher than normal
- ABS or traction-control warning light may illuminate
Common causes
Most likely first
- Faulty brake booster pressure sensorLikely
- Damaged wiring or poor connection in the sensor circuitCommon
- Failed brake booster (loss of vacuum/pressure assist)Common
How to diagnose & fix
Work through it in order
- Scan for related brake and ABS codes and read freeze-frame data.
- Inspect the sensor connector and wiring for damage, corrosion, or looseness.
- Compare the sensor's reading against the actual booster pressure to confirm it is out of range.
- Replace the brake booster pressure sensor if it reads incorrectly.
- If the booster itself is not holding pressure, replace the booster.
FAQ
Quick answers
Is it safe to drive with P0556?+
Can I just clear P0556?+
Related codes
Read & clear P0556 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.