P0555

Code

Generic P — Powertrain

Brake Booster Pressure Sensor Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 79 RU: 39

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Brake warning lamp or ABS/ traction/brake system light illuminated
MIL (Check Engine Light) may be set if PCM uses booster sensor for engine management
Hard or increased brake pedal effort / reduced power assist if vacuum is actually low
Longer brake pedal travel or inconsistent pedal feel (if vacuum supply is affected)
Rough idle, stalling, or poor engine performance if vacuum leak is present
Stored freeze-frame data showing related engine/load conditions

Scan for freeze-frame and all stored codes; note related codes (vacuum, MAP, idle)
Visually inspect sensor, vacuum hoses and connectors for damage, corrosion or disconnection
Backprobe sensor connector and check for proper reference voltage (typically 5V) and a good ground at the sensor pin
Measure sensor signal voltage while engine idles and while applying brake pedal or varying engine load; note that voltage should change smoothly
Check continuity and resistance between sensor pins and PCM connector; inspect for shorts to battery or ground
Pressure/vacuum check of booster supply hose and intake manifold to verify vacuum integrity

Most brake booster pressure sensors use a 5V reference and provide a 0.5–4.5V signal proportional to pressure/vacuum (exact range is vehicle-specific)
Expected behavior: signal voltage changes smoothly with vacuum level and with engine load/pedal application
Common fault readings: constant voltage stuck near 0V or reference voltage, rapid voltage fluctuation, or no change when vacuum changes
Resistance/impedance is typically in the kilo-ohm range for the sensing element (check OEM spec)

Retrieve and record code(s) and freeze-frame data using a scan tool. Identify any related MAP/vacuum or idle codes.
Visually inspect sensor, vacuum lines and electrical connectors for damage, contamination, loose pins or corrosion.
With ignition ON (engine off), backprobe the sensor connector: verify 5V reference (if used), sensor ground, and baseline signal voltage. Compare to spec.
Start engine and observe live sensor voltage while varying engine speed and applying brake pedal; signal should move smoothly. Note any stuck or erratic values.
Check continuity between sensor ground/reference and PCM pins; look for shorts to battery or chassis ground.
Pressure/vacuum test the booster supply hose and intake manifold for leaks; repair any vacuum leaks and re-test sensor behavior.
If wiring and vacuum supply check OK but signal is out of range, swap with known-good sensor or bench-test/replace sensor.
Repair any wiring/connectors as needed, clear codes, perform road test and re-scan to confirm the fault does not return. If intermittent and no wiring/sensor fault is found, consider PCM input testing/diagnosis by qualified technician.