P0559
Brake Booster Pressure Sensor Circuit Intermittent
Powertrain Chassis/Safety Brake System 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The brake booster pressure sensor is sending an inconsistent or intermittent signal to the engine computer, like a loose phone connection that keeps dropping. This prevents the ECU from reliably monitoring vacuum pressure in the brake booster system.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminates intermittently
Hard brake pedal feel or increased pedal effort
Brake warning light may appear on dashboard
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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 should vary smoothly between 0.5V and 4.5V based on vacuum levels. When the signal drops out, spikes, or behaves erratically, the ECU detects an intermittent circuit condition and stores this fault code.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Voltage 0.5V to 4.5V (linear with vacuum) Erratic/missing signal or out-of-range spikes
Signal Consistency Smooth transition over time Dropouts or electrical noise detected
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Connector and wiring harness
Inspect the brake booster sensor connector for corrosion, loose pins, or water damage; reseat the connector firmly.
2
Brake booster hose
Check vacuum hose from engine to brake booster for cracks or loose connections causing air leaks.
3
Brake booster pressure sensor
Replace the sensor if connector and hose are secure but the intermittent fault persists.