Code Definition

P0556 — Brake Booster Pressure Sensor Signal Out of Range

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0556

P0556 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0556 is stored, the module has detected a plausibility fault — the measured value is in the electrical range but is not consistent with expected operating behaviour; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0556 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

Fault code P0556 is set when the vehicle's powertrain control module (PCM) detects that the signal from the brake booster pressure sensor is outside of the expected range. This sensor measures the vacuum pressure in the brake booster, which is essential for power-assisted braking. An out-of-range signal can indicate either too high or too low pressure compared to what is expected under normal conditions. Such a discrepancy could be due to a malfunctioning sensor, issues in the brake booster system, or problems in the sensor's electrical circuit.

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