P0559

Code

Generic P — Powertrain

Brake Booster Pressure Sensor Circuit Intermittent

Brand: Generic

Type: P — Powertrain

Views: UK: 18 EN: 38 RU: 22

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Page language: EN

Causes

Corroded or loose sensor connector
Damaged/frayed wiring harness or intermittent open/short
Faulty brake booster pressure (vacuum) sensor
Vacuum leak or degraded vacuum hose to booster
Failed brake booster (diaphragm leak or internal fault)
Poor sensor ground or reference voltage fluctuation

Symptoms

MIL/Check Engine Light illuminated intermittently
Brake pedal may feel harder than normal (reduced power assist) when booster loses vacuum
Intermittent idle problems, rough idle or stalling when vacuum is lost
Hissing sound from vacuum line or brake booster
Inconsistent brake assist felt under certain conditions

What to check

Scan for P0559 and any related codes; record freeze frame and occurrence count
Visually inspect sensor, connector, wiring harness, and vacuum lines for damage or corrosion
Backprobe sensor connector and check reference voltage, signal voltage, and ground with key ON
Wiggle harness/connector while monitoring live data to reproduce intermittent behavior
Pressure/vacuum test the booster supply (vacuum gauge) and check check-valve operation
Inspect brake booster for external damage and test for diaphragm leaks (bench test or vacuum gauge)

Signal parameters

Typical sensor supply/reference: ~5 V (varies by vehicle) — verify with manufacturer data
Signal output typically varies within a 0.5–4.5 V range corresponding to vacuum/pressure (vehicle-specific)
At key ON engine OFF the sensor should produce a stable idle/ambient reading; values should change smoothly with engine vacuum
Open circuit or intermittent connection may show sudden jumps to near 0 V or to reference voltage, or erratic readings

Diagnostic algorithm

Retrieve and record code, freeze frame, and any other stored DTCs. Clear codes and attempt to reproduce.
Perform a visual inspection of the sensor, connector, and vacuum hose to the booster. Repair/replace damaged vacuum lines or connectors as found.
Backprobe sensor connector: with key ON (engine OFF) verify reference voltage, signal voltage stability, and ground continuity to chassis/PCM. Compare to vehicle-specific values.
Start engine and observe live data while commanding changes to engine load/throttle. The sensor signal should respond smoothly to vacuum changes. Wiggle harness/connectors during test to look for intermittent changes.
Pressure/vacuum test booster supply with a gauge. Verify check-valve and vacuum level under idle and during engine off. Repair booster or vacuum supply if vacuum is unstable or insufficient.
If wiring or connector faults are found, repair or replace affected wiring and connectors; protect and secure harness to prevent recurrence.
If wiring and vacuum supply are good but the signal remains intermittent, replace the brake booster pressure sensor.
If a new sensor does not cure the intermittent condition and wiring checks are good, investigate PCM input circuitry or seek manufacturer guidance for module tests.
After repairs, clear codes and perform road test to confirm the fault does not return and that brake assist and idle behavior are normal.

Likely causes

Connector pushed back, pins bent or corroded at sensor
Wire chafing at harness rub point causing intermittent contact
Sensor internal connector corrosion from moisture
Loose vacuum hose or cracked check valve causing variable vacuum
Failed sensor electronics causing intermittent output
Weak/dirty ground at booster/sensor mounting

Fault status

⚠️ Status

Intermittent fault detected on the brake booster pressure sensor circuit. PCM observed unstable or sporadic sensor signal; DTC set when irregular readings exceed threshold. Check wiring, connectors, vacuum supply, and sensor.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours