English-first OBD-II diagnostics Static, fast, focused lookup pages
CD CheckDTC Garage-grade fault lookup
Browse codes Try AI Diagnose
Home / Codes / P0559
DTC code page

P0559: Brake Booster Pressure Sensor Circuit Intermittent

Quick answer: The brake booster pressure sensor signal is dropping in and out or behaving inconsistently.

Drivers also search this fault as brake booster pressure sensor intermittent, intermittent brake booster pressure code, P0559 code.

Severity: high Family: powertrain Related paths: 12
Meaning

What P0559 usually means

P0559 is often the most frustrating brake-booster pressure code because intermittent faults rarely misbehave on command in the driveway. The PCM is seeing the booster pressure signal move erratically, disappear briefly, or behave in a way that does not stay stable enough to trust. Sometimes the root cause is a loose connector or broken wire near the booster. Other times vibration, heat, or an intermittent vacuum leak makes the pressure story look irrational only during certain brake applications or idle conditions. That makes P0559 valuable for SEO and useful for readers because it speaks directly to the stop-and-start nature of the complaint.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Ask whether the hard pedal or idle issue comes and goes. That timing is a major clue with P0559.
  • Wiggle-test the connector and inspect harness routing near moving engine parts and hot components.
  • Do not ignore intermittent hissing or brake-assist changes after one or two pedal applications.
Driving risk

Can you keep driving?

If brake assist sometimes drops out or the pedal goes hard unpredictably, treat P0559 as a safety-relevant fault. Drive only as needed until the intermittent cause is proven.

High urgency: If symptoms are active, reduce driving and diagnose quickly before secondary damage builds.
Symptoms

Common symptoms

Likely causes

Common causes behind this code

  • Intermittent brake booster pressure sensor internal failure
  • Loose, corroded, or vibration-sensitive connector terminals
  • Harness damage that opens or shorts as the engine moves
  • Vacuum hose, booster, or check-valve leak that appears only under certain conditions
  • Engine vacuum instability creating a sensor pattern the PCM cannot trust

Cause phrases often tied to this code: loose connector, intermittent wiring fault, bad brake booster pressure sensor, vacuum hose leak, check valve problem.

Diagnostic order

Suggested workflow

  1. Inspect the sensor connector, pin tension, and nearby harness for movement-related faults.
  2. Check booster hose and check-valve integrity for leaks that only appear under vacuum change.
  3. Monitor live data while applying the brake and changing engine speed to see whether the signal drops out.
  4. Verify reference voltage and ground stability under the same conditions that trigger the complaint.
  5. Repair the proven intermittent sensor, wiring, or vacuum issue and confirm the signal stays stable.
Avoid guesswork

Common mistakes

  • Replacing the sensor without touching the connector or harness.
  • Ignoring intermittent vacuum leaks because they are quiet during a quick visual inspection.
  • Clearing the code and sending the car out without recreating the conditions that triggered it.
Repair path

Practical fix guidance

  • Fix the verified intermittent sensor, connector, harness, check-valve, or vacuum-hose fault.
  • After repair, recheck pedal feel and idle quality during repeated brake applications and hot idle.
  • If symptoms remain inconsistent, continue with movement and heat-related harness testing instead of guessing.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0559

Useful when the driver knows the wording but not the exact DTC yet.

  • brake booster pressure sensor intermittent
  • intermittent brake booster pressure code
  • P0559 code
Related search intent

Queries this page can answer naturally

  • P0559 code meaning
  • what does P0559 mean
  • brake booster pressure intermittent
  • P0559 hard brake pedal
FAQ

Quick questions about P0559

Why is P0559 harder to diagnose than P0558?

Because the signal fault is intermittent, so the wiring or vacuum problem may only appear with heat, vibration, or certain brake events.

Can P0559 be only a connector issue?

Yes. Loose or corroded terminals are common intermittent causes.

Should I ignore P0559 if the brakes feel normal right now?

No. Intermittent brake-assist faults can return when you need the brakes most.