P0559

Universal

Brake Booster Pressure Sensor Circuit Intermittent

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
High Severity

The vehicle has detected an intermittent signal in the brake booster pressure sensor circuit. This sensor helps the vehicle monitor pressure in the brake booster, which supports braking assistance. A signal that comes and goes may trigger a warning or affect how the system monitors brake assist, but the code alone does not prove the sensor needs replacement.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the brake pedal suddenly feels harder, braking assistance seems reduced, or a brake warning appears, pull over safely and arrange professional help rather than continuing to drive. If braking feels normal and no warning is present, have the fault diagnosed promptly; do not rely on this code alone to judge whether the vehicle is safe.

Common Symptoms

  • The check-engine or another system warning light may appear, depending on the vehicle.
  • There may be no noticeable symptoms if the signal interruption is brief or the vehicle does not show a clear change in brake assist.
  • Brake assist may feel inconsistent if the fault affects the vehicle's monitoring or operation of the assist system.
  • A harder-than-usual brake pedal or reduced assist can occur if there is a related booster-system problem, but this code by itself does not confirm that condition.

Common Causes

  • A loose, corroded, damaged, or intermittently connected sensor connector.
  • Damaged wiring, a poor electrical connection, or a harness that intermittently opens or shorts.
  • An intermittent fault inside the brake booster pressure sensor.
  • A problem with the sensor's power, ground, or signal circuit.
  • A less common control-module or related-system fault, or a separate booster pressure problem affecting the signal.

Diagnostic Steps

  1. Note any warning lights and whether the brake pedal feels different. If braking assistance seems reduced or the pedal feels unusually hard, stop driving when safe and seek professional help.
  2. With the vehicle parked safely and the ignition off, visually check accessible wiring and connectors around the relevant brake booster sensor area for looseness, visible damage, or corrosion. Do not pull on wiring or disconnect components unless the vehicle-specific instructions allow it.
  3. Check the owner’s manual for the meaning of any brake or system warning and whether it advises against driving.
  4. If you have a compatible scan tool, record the code and any related codes before clearing anything; related codes can help narrow the fault.
  5. Have a technician perform vehicle-specific circuit and scan-data tests if the warning returns or the cause is not obvious. Avoid probing safety-related circuits without the correct information and equipment.

When to Call a Professional

Use a compatible scan tool to check related codes and, where supported, monitor the sensor signal for dropouts. Inspect the circuit and connectors using the vehicle-specific wiring information, and test power, ground, wiring continuity, and signal behavior as applicable. Confirm the sensor and booster system operation before replacing parts; exact procedures depend on the vehicle.

Compare component listings

Confirm diagnosis and vehicle fitment before buying. A listing does not prove that a part needs replacement. We may earn a commission from qualifying purchases.

Search Amazon Search eBay

Commonly Asked Questions

Does P0559 prove the brake booster pressure sensor is bad?

No. It identifies an intermittent condition in the sensor circuit. Wiring, connectors, power, ground, or another related fault can produce the same detected condition.

Does this code mean the brakes have failed?

Not by itself. It does not establish that braking has failed, but a related problem could affect brake assist. Treat a hard pedal, reduced assist, or a brake warning as a safety concern.

Can I keep driving with P0559?

The code alone cannot determine whether the vehicle is safe to drive. If the pedal feels unusual, assist seems reduced, or a brake warning is on, stop when safe and arrange professional assistance. Otherwise, get the fault checked promptly.

What does intermittent mean here?

The sensor circuit signal may be present at some times and missing or abnormal at others. A loose connection or damaged wire can cause this, as can an intermittent sensor fault.

Will replacing the sensor necessarily fix P0559?

No. Diagnosis should check the sensor and its circuit before parts are replaced. The applicable tests and repair steps depend on the vehicle's model, year, and engine.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.