P0559 – Brake Booster Pressure Sensor Circuit Intermittent

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit Intermittent

Definition source: SAE J2012/J2012DA (industry standard)

P0559 indicates the powertrain control module has detected an intermittent condition in the brake booster pressure sensor circuit. “Intermittent” means the signal or circuit integrity is unstable at times rather than consistently failed, so the concern may appear and disappear with vibration, temperature changes, or specific operating conditions. Because monitoring strategy, wiring layout, and scan tool data labels vary by vehicle, confirm the sensor location, pinout, and test procedure in the correct service information before testing. Treat this DTC as an electrical/signal fault until you verify a mechanical or hydraulic issue with targeted checks and repeatable test results.

What Does P0559 Mean?

P0559 – Brake Booster Pressure Sensor Circuit Intermittent means the control module has identified an intermittent (unstable, momentary, or dropout) electrical condition in the brake booster pressure sensor circuit. Under SAE J2012 DTC conventions, the code points to a specific monitored circuit where the module expects a plausible, continuous signal. When the module sees the brake booster pressure sensor signal behave erratically—such as brief dropouts, sudden spikes, or loss of correlation consistent with an intermittent circuit connection—it can set P0559 and may store freeze-frame data for the event.

Quick Reference

  • Subsystem: Brake booster pressure sensor circuit (signal, reference, and ground paths as applicable).
  • Common triggers: Momentary signal dropouts, poor terminal contact, vibration-sensitive opens/shorts, moisture intrusion, or unstable power/ground to the sensor.
  • Likely root-cause buckets: Wiring/connector/terminal fit, sensor internal fault, shared reference/ground issues, power supply faults, module or harness routing issues.
  • Severity: Potentially safety-relevant; may affect brake assist-related monitoring and can illuminate warnings depending on vehicle strategy.
  • First checks: Scan for related codes, review freeze-frame, inspect connector/harness at the sensor and along routing, check for loose pins and corrosion.
  • Common mistakes: Replacing the sensor without verifying intermittent wiring/terminal issues or ignoring shared power/ground problems affecting multiple sensors.

Theory of Operation

The brake booster pressure sensor provides the control module with an electrical signal representing booster pressure (or vacuum/pressure differential, depending on design). The sensor is typically supplied by a regulated reference and a dedicated sensor ground (or other supply/return arrangement that varies by vehicle), and it outputs a varying signal the module samples repeatedly. The module uses this input for monitoring and plausibility checks related to brake assist conditions and system diagnostics.

P0559 sets when the module detects the circuit is not consistently stable—such as brief signal loss, sudden discontinuities, or noise consistent with an intermittent open, short, or poor connection. Because the event may be brief, the fault can be difficult to duplicate unless the harness is disturbed or conditions match the original trigger, so repeatable testing and careful inspection are essential.

Symptoms

  • Warning light illuminated malfunction indicator or brake-related warning messages (varies by vehicle).
  • Intermittent faults that come and go, often after bumps, vibration, or temperature changes.
  • Stored freeze-frame data showing the fault occurred during braking events or specific driving conditions.
  • Reduced assist message or brake system status indicators may appear on some platforms (strategy varies by vehicle).
  • Scan data anomalies where brake booster pressure parameter briefly drops out, spikes, or becomes erratic.
  • Multiple sensor codes if a shared reference or sensor ground is intermittently disturbed.

Common Causes

  • Intermittent open or high resistance in the brake booster pressure sensor signal circuit (chafed wiring, broken conductor inside insulation)
  • Loose, corroded, contaminated, or partially backed-out terminals at the brake booster pressure sensor connector
  • Poor power or ground feed to the brake booster pressure sensor (intermittent loss due to connector/terminal issues)
  • Harness routing issues causing intermittent contact (rub-through points, pinch points, vibration-related movement near brackets or heat sources)
  • Brake booster pressure sensor internal fault causing dropouts or momentary invalid output
  • Intermittent issue at the control module connector (terminal tension, moisture intrusion, connector not fully seated)
  • Shared reference or sensor ground circuit intermittently disturbed by another component on the same circuit (varies by vehicle)
  • Control module software/logic sensitivity or internal fault (less common; confirm only after circuit and sensor checks)

Diagnosis Steps

Tools that help: a scan tool capable of reading live data and freeze-frame, a digital multimeter, and basic back-probing tools. A wiring diagram and service information are important because sensor pinouts and shared circuits vary by vehicle. If available, use a breakout lead or test harness to reduce terminal damage, and have supplies for connector cleaning and terminal inspection.

  1. Confirm the code and capture context: Scan all modules, record P0559, freeze-frame data, and any related codes. Note whether the code is current, pending, or history, because intermittent faults often set as pending first.
  2. Check for related power/ground or network codes: Address any codes indicating unstable module power, sensor reference issues, or communication problems first, since they can create intermittent sensor-circuit symptoms.
  3. Review service information for the exact circuit: Identify the brake booster pressure sensor pins (power, ground, signal, and any reference circuit) and any splices or shared grounds. This prevents mis-testing the wrong circuit.
  4. Perform a focused visual inspection: Inspect the sensor, its connector, and the harness routing. Look for rubbing, heat damage, tight bends, recent repairs, or areas where the harness can move with engine vibration or body flex. Correct obvious issues before deeper testing.
  5. Inspect connector integrity and terminals: With the connector disconnected, check for corrosion, moisture, damaged seals, terminal spread, push-back, or poor pin fit. Reseat the connector and ensure locks are fully engaged. Repair terminal issues as needed.
  6. Live-data check for dropouts: On the scan tool, monitor the brake booster pressure sensor parameter(s) at idle and during gentle changes in operating conditions as allowed by service procedures. Look for momentary spikes, dropouts, or implausible jumps that coincide with the fault setting.
  7. Wiggle test with logging: While logging live data (and/or pending DTC status), gently manipulate the harness and connector at the sensor, along the harness routing, and at the module connector area. If the signal drops out or becomes erratic during movement, isolate the exact location where the behavior changes.
  8. Power and ground verification under load: Use the multimeter to verify the sensor’s power feed and ground integrity. Do not rely only on static checks; apply an appropriate load per service information and confirm the circuit remains stable when the fault is likely to occur.
  9. Voltage-drop test the ground and feed circuits: With the circuit operating, perform voltage-drop testing across the sensor ground path and the sensor supply path to identify excessive resistance that may appear only intermittently. Move the harness during the test to catch vibration-related changes.
  10. Signal circuit continuity and intermittent-open checks: If access allows, check the signal circuit from sensor to module for continuity and for intermittent opens/shorts by flexing the harness and checking for instability. If the circuit shares a splice, inspect and test the splice point (varies by vehicle).
  11. Differentiate sensor vs. wiring: If power/ground are stable and the signal circuit passes integrity checks, suspect an intermittent sensor output. If the sensor output becomes unstable only when the harness/connector is moved, prioritize wiring/terminal repairs over sensor replacement.
  12. Clear, verify, and confirm the repair: Clear codes, perform the service-information-defined confirmation procedure or drive cycle, and recheck for pending codes and stable live data. Ensure the condition does not return under the same operating context captured in freeze-frame.

Professional tip: Intermittent circuit faults are easiest to prove when you can reproduce them. Use scan-tool data logging during a controlled wiggle test and pair it with voltage-drop measurements on the sensor feed and ground. If the sensor value glitches at the same moment a feed/ground drop is observed, you’ve confirmed a circuit problem rather than guessing at a sensor.

Need wiring diagrams and factory-style repair steps?

Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.

Factory repair manual access for P0559

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for P0559 vary widely because the fault is intermittent and may require time to reproduce. The final cost depends on what testing confirms (wiring vs sensor vs module), parts accessibility, and labor time needed to verify the repair.

  • Repair wiring damage such as chafed insulation, stretched conductors, or broken strands in the brake booster pressure sensor signal, reference, or ground circuits
  • Clean and secure connectors by addressing corrosion, moisture intrusion, poor terminal tension, and improper locking at the sensor and module connectors
  • Restore power/ground integrity by repairing shared grounds, splice points, or power feeds that intermittently drop out under vibration or load
  • Replace the brake booster pressure sensor only after confirming the sensor output intermittently glitches or drops out while power/ground and wiring remain stable
  • Repair terminal fit issues by correcting pin fitment problems, backed-out terminals, or damaged connector housings causing momentary opens
  • Update or reprogram the control module if service information indicates a calibration or logic update is required and all circuit checks pass
  • Replace the control module only after ruling out sensor and harness faults and confirming an internal intermittent input fault per service procedures

Can I Still Drive With P0559?

P0559 indicates an intermittent brake booster pressure sensor circuit problem, so braking-assist related behavior may be inconsistent depending on when the signal drops out. If you notice a brake warning message, a hard brake pedal, increased stopping distance, reduced engine power, or any change in brake feel, do not continue driving—have the vehicle inspected and towed if needed. If no symptoms are present, drive cautiously and prioritize diagnosis soon, since intermittent faults can become continuous without warning.

What Happens If You Ignore P0559?

If P0559 is ignored, the intermittent signal can progress to a more frequent dropout, potentially triggering warning lights, disabling certain brake-assist or stability-related functions (varies by vehicle), and causing unpredictable assist behavior. The vehicle may store additional fault codes, and repeated circuit interruptions can lead to unnecessary parts replacement if the underlying wiring/connector issue is not corrected.

Compare nearby brake pressure trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0555 – Brake Booster Pressure Sensor Circuit
  • P0936 – Hydraulic Pressure Sensor Circuit Intermittent
  • P0539 – A/C Evaporator Temperature Sensor Circuit Intermittent
  • P0809 – Clutch Position Sensor Circuit Intermittent
  • P051B – Crankcase Pressure Sensor Circuit Range/Performance
  • P0908 – Gate Select Position Circuit Intermittent

Key Takeaways

  • P0559 is an intermittent circuit DTC tied to the brake booster pressure sensor signal path, not a confirmed mechanical brake booster failure by itself
  • Intermittent faults are often wiring/connector related (pin fit, corrosion, harness movement) and require reproduction and inspection under vibration/heat
  • Confirm power and ground stability first before condemning the sensor or control module
  • Use live-data logging and wiggle testing to catch brief dropouts that a quick driveway test may miss
  • Safety comes first—any change in brake feel or brake warnings should be treated as a stop-driving condition

Vehicles Commonly Affected by P0559

  • Vehicles with electronically monitored brake assist that use a brake booster pressure sensor input for control decisions
  • Vehicles with integrated stability/traction systems that depend on accurate booster pressure information (implementation varies by vehicle)
  • High-mileage vehicles where harness flexing and terminal tension loss are more likely
  • Vehicles exposed to moisture/corrosion where connector contamination can cause intermittent electrical contact
  • Vehicles with recent repairs near the booster, master cylinder area, or main harness routing where connectors may be disturbed
  • Vehicles with tight engine-bay packaging where harnesses can rub on brackets or heat sources and intermittently short or open
  • Vehicles used on rough roads where vibration can reveal marginal terminals or broken conductor strands
  • Vehicles with prior collision or engine-bay work that may have stressed wiring looms or splice points

FAQ

Does P0559 mean the brake booster is bad?

No. P0559 means the brake booster pressure sensor circuit signal is intermittent. The root cause may be the sensor, wiring, connectors, power/ground feeds, or less commonly the control module. Confirm with circuit testing before replacing parts.

Why does the code come and go?

Intermittent DTCs commonly appear only when conditions align—vibration, temperature changes, moisture, or harness movement can briefly interrupt the signal or create momentary shorts/opens. This is why inspection and testing during a wiggle test and road-test logging are often necessary.

Will clearing P0559 fix it?

Clearing the code only erases stored data; it does not correct the intermittent circuit condition. If the underlying issue remains, the monitor is likely to fail again and the code will return once the fault reoccurs.

What should be checked first for an intermittent circuit fault?

Start with the basics: connector seating/locks, terminal tension, corrosion or moisture, harness chafing, and shared power/ground points. Then verify stable reference voltage, ground integrity, and signal continuity while manipulating the harness and monitoring live data.

Can a weak battery cause P0559?

Low system voltage or unstable power/ground can contribute to intermittent sensor circuit behavior on some platforms, but it should not be assumed. Test battery/charging health and confirm the sensor’s power and ground remain stable during cranking and under load using the procedures in service information.

Always verify the exact diagnostic and repair procedure for your vehicle using the correct service information, since monitor logic, wiring routes, and safety-related responses to P0559 vary by platform.