P0556
Brake Booster Pressure Sensor Circuit Range/Performance
Brakes / booster
Generic OBD-II
High
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.
High
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.
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?+
The brakes still function, but assist may be reduced and pedal feel can change. Drive gently and get it inspected soon, since anything affecting braking is a safety concern.
Can I just clear P0556?+
It will return until the sensor, wiring, or booster is repaired. Because it involves the brake system, don't ignore it.
Related codes
Often seen with P0556
Read & clear P0556 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX