P0555
Brake Booster Pressure Sensor Circuit
Powertrain Chassis/Safety Brake Booster Sensor 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your brake booster pressure sensor isn't sending the right signal to the engine computer, like a broken gauge telling you incorrect tire pressure. The ECU can't verify the brake system's vacuum pressure, so it triggers a fault code.

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Symptoms You May Notice
3 known symptoms for this code
Hard brake pedal requiring excessive pressure to stop
Check Engine Light illuminates
Brake system warning light may appear on dash
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage output from the brake booster pressure sensor, which measures vacuum pressure in the brake booster. The sensor should produce a voltage signal proportional to booster vacuum (typically 0.5-4.5V). If the signal is out of range, shorted, open, or missing, the ECU sets P0555.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Voltage 0.5V to 4.5V proportional to vacuum Below 0.1V or above 4.9V
Pressure Range 15-20 inHg vacuum at idle Erratic or no pressure signal detected
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Brake booster vacuum hose
Inspect hose for cracks, splits, or loose connections; reseat or replace if damaged.
2
Sensor connector and wiring
Check connector pins for corrosion, loose terminals, or water intrusion; clean or reseat connections.
3
Brake booster pressure sensor
If voltage reading is out of range after checking hose and wiring, replace the sensor itself.