P0555

Brake Booster Pressure Sensor Circuit

Powertrain Chassis/Safety Brake Booster Sensor 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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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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How Your ECU Detects This

Technical sensor logic and voltage thresholds

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

ParameterNormal RangeFault 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.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0555 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code P0555

What happens after you fix the fault

Once the fault is repaired, P0555 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.