P0555 – Brake Booster Pressure Sensor Circuit

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

Definition source: SAE J2012/J2012DA (industry standard)

P0555 is a powertrain diagnostic trouble code indicating the control module has detected a fault in the brake booster pressure sensor circuit. This is a circuit-related code, meaning the module is reacting to an electrical or signal integrity problem (such as an open, short, poor connection, or unexpected signal behavior) rather than confirming a mechanical brake or booster failure by itself. Depending on how the vehicle is designed, the brake booster pressure signal may be used for brake assist monitoring, plausibility checks, and coordination with other safety or drivability functions. DTC behavior, default strategies, and the exact enable conditions for the monitor vary by vehicle, so confirm the circuit layout, pinouts, and test specifications in the appropriate service information.

What Does P0555 Mean?

P0555 – Brake Booster Pressure Sensor Circuit means the powertrain control module has identified a malfunction associated with the electrical circuit for the brake booster pressure sensor. Under SAE J2012 DTC conventions, the code points to a defined fault entry related to the sensor’s circuit, not a guarantee that the sensor itself is failed. The module typically expects a coherent, stable signal from the brake booster pressure sensor and also expects the associated power, ground, and signal circuits to remain within valid operating conditions. If the module detects an abnormal circuit condition or signal that does not meet its internal diagnostics, it can set P0555 and may command warning indicators or a fallback strategy (varies by vehicle).

Quick Reference

  • Subsystem: Brake booster pressure sensor circuit (sensor signal, power feed, ground, and related wiring to the control module).
  • Common triggers: Open/short in the signal circuit, poor connector contact, sensor power/ground fault, intermittent wiring faults, or signal irregularities detected during self-tests.
  • Likely root-cause buckets: Wiring/connector issues, sensor internal fault, power/ground distribution problem, module input circuit concern, or calibration/software-related diagnostic sensitivity (varies by vehicle).
  • Severity: Potential safety impact; the vehicle may alter brake-assist monitoring, illuminate warnings, and in some designs affect related stability/assist functions.
  • First checks: Verify stored codes and freeze-frame data, inspect harness/connector condition and routing, check for loose pins/corrosion, and confirm power and ground integrity at the sensor.
  • Common mistakes: Replacing the sensor without verifying circuit integrity, overlooking intermittent opens near connectors, skipping voltage-drop checks on grounds, or ignoring shared reference/ground faults affecting multiple sensors.

Theory of Operation

The brake booster pressure sensor provides the control module with an electrical signal representing pressure (or vacuum/pressure state, depending on design) in the brake booster system. The sensor is typically supplied by a regulated reference or feed voltage and a dedicated ground, and it returns a signal voltage that changes with booster pressure. The module continuously monitors this signal for electrical integrity and plausibility, using internal diagnostics to confirm the signal responds and remains within expected electrical behavior.

If the signal becomes unreliable due to an open circuit, short to power or ground, excessive resistance, poor terminal contact, or unstable power/ground, the module may detect an abnormal circuit condition and set P0555. Some platforms also perform rationality checks against other inputs during braking events; however, P0555 remains a circuit fault classification, so testing should focus on the sensor circuit’s electrical health.

Symptoms

  • Warning light: Malfunction indicator lamp illuminated; brake-related warnings may also appear (varies by vehicle).
  • Stored faults: Additional diagnostic codes for related sensors or reference/ground circuits may be present.
  • Assist limitations: Reduced or altered brake-assist monitoring or related assist features may be disabled (varies by vehicle).
  • ABS/traction messages: Stability/traction/ABS indicators or messages may appear if the signal is shared for plausibility (varies by vehicle).
  • Intermittent behavior: Symptoms may come and go with vibration, temperature changes, or steering/brake pedal movement affecting harness routing.
  • Driveability changes: In some designs, the module may use a fallback strategy that changes response during braking or deceleration (varies by vehicle).

Common Causes

  • Damaged wiring harness to the brake booster pressure sensor (chafing, pinched section, heat damage)
  • Connector problems at the sensor or control module (loose fit, backed-out pin, corrosion, moisture intrusion)
  • Open circuit in the sensor signal, reference, or ground path (broken conductor, poor crimp, internal wire break)
  • Short to ground or short to power affecting the sensor signal circuit (rub-through to chassis, contact with another circuit)
  • Poor power or ground quality feeding the sensor circuit (high resistance in shared grounds, weak ground point, blown/loose fuse depending on design)
  • Brake booster pressure sensor internal electrical fault (out-of-range output caused by internal circuit failure)
  • Control module input fault or internal issue (less common; confirm all external circuits first)
  • Aftermarket wiring changes or recent repairs near the booster/sensor circuit introducing misrouting or damaged terminals

Diagnosis Steps

Tools typically needed include a scan tool capable of reading freeze-frame and live data, a digital multimeter, and basic hand tools for connector access. A wiring diagram and connector pinout from service information are strongly recommended because routing and pin assignments vary by vehicle. If available, use back-probing leads and terminal tools to avoid spreading or damaging terminals during testing.

  1. Confirm DTC P0555 is active or stored, and record freeze-frame data and any accompanying codes. Address power supply, communication, or module voltage codes first because they can skew sensor-circuit monitoring.
  2. Use the scan tool to review live data related to the brake booster pressure sensor (naming varies by vehicle). Note whether the parameter appears implausible, fixed, intermittent, or drops out. Save a short data log for comparison after repairs.
  3. Perform a thorough visual inspection of the sensor area and harness routing. Look for rubbing points, stretched sections, contact with sharp edges, and signs of fluid contamination. Verify the connector is fully seated and locked.
  4. Key off, then disconnect the sensor connector and inspect terminals closely. Check for corrosion, moisture, bent pins, pushed-back terminals, and poor pin tension. Repair terminal issues before deeper electrical testing.
  5. With the sensor still disconnected, check the harness side for obvious opens/shorts using multimeter continuity tests as guided by service information. Verify the signal circuit is not shorted to ground or to power, and verify it is not shorted to adjacent circuits.
  6. Check sensor circuit power/reference and ground integrity at the harness connector with the ignition on (as applicable). Compare findings to service information expectations. If power/reference is missing, trace back to the supplying circuit (fuse, splice, shared reference line) and correct the root cause.
  7. Perform voltage-drop testing on the sensor ground path under operating conditions (ignition on; engine state varies by vehicle). Excessive drop indicates unwanted resistance in the ground circuit, connectors, splices, or ground point. Repair the high-resistance location rather than replacing the sensor preemptively.
  8. Wiggle test: with the scan tool logging live data, manipulate the harness and connector (near the sensor, along routing, and near the module). Watch for sudden changes, dropouts, or spikes. If the fault is induced, isolate the exact section and repair the wiring/terminal fitment.
  9. If wiring, power/reference, and ground check out, test the sensor according to service information. Depending on design, this may include checking signal response while conditions change and verifying the circuit returns to a stable reading without dropouts. Replace the sensor only if it fails the specified tests.
  10. If the sensor and all external circuits pass and P0555 returns, verify module connector condition (pin fit, corrosion, water intrusion) and re-check circuit integrity end-to-end. Only after confirming all external causes should module-related faults be considered, following service information procedures.

Professional tip: Intermittent circuit faults are often terminal-tension or harness-rub issues that won’t show up on a simple continuity check. Prioritize live-data logging plus a controlled wiggle test, and use voltage-drop testing on power and ground paths to find high resistance that can trigger the brake booster pressure sensor circuit monitor without leaving obvious visual damage.

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 P0555

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for P0555 vary widely by vehicle and depend on what testing confirms in the brake booster pressure sensor circuit, along with parts access, wiring condition, and labor time. Diagnose first so the repair targets the verified electrical fault rather than replacing components unnecessarily.

  • Repair or replace damaged wiring in the brake booster pressure sensor circuit (chafing, pinched sections, melted insulation)
  • Clean, repair, or replace affected connectors/terminals (corrosion, moisture intrusion, loose pin fit, bent pins)
  • Restore proper power supply and ground to the sensor circuit (repair opens, high resistance, or poor ground points)
  • Replace the brake booster pressure sensor only after circuit integrity and supply/ground checks pass
  • Repair circuit shorts (short-to-ground or short-to-power) found during isolation testing
  • If confirmed by pinpoint tests, address control module connector issues or required programming/configuration per service information

Can I Still Drive With P0555?

P0555 indicates an electrical fault in the brake booster pressure sensor circuit, and the practical risk depends on how the vehicle uses that signal. Because braking performance and brake-assist related functions can be affected on some designs, treat this as safety-relevant. If you notice a hard brake pedal, reduced brake assist, warning indicators related to braking/stability, or any unexpected changes in braking feel, do not continue driving; have the vehicle inspected and repaired. If the vehicle seems to stop normally, drive only as needed and schedule prompt diagnosis.

What Happens If You Ignore P0555?

Ignoring P0555 can lead to continued warning lights and the possible disabling or limiting of brake-assist related strategies that rely on the brake booster pressure sensor circuit. Intermittent circuit faults may worsen over time, potentially causing more frequent warnings or reduced confidence in braking-related features. Ongoing electrical issues can also create secondary faults and complicate later diagnosis, especially if wiring damage progresses or corrosion spreads in connectors.

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

  • P0559 – Brake Booster Pressure Sensor Circuit Intermittent
  • P0932 – Hydraulic Pressure Sensor Circuit
  • P0520 – Engine Oil Pressure Sensor/Switch Circuit
  • P0535 – A/C Evaporator Temperature Sensor Circuit
  • P0515 – Battery Temperature Sensor Circuit
  • P0571 – Brake Switch “A” Circuit

Key Takeaways

  • P0555 is defined as a fault in the brake booster pressure sensor circuit, not a confirmed mechanical brake booster failure.
  • Most successful repairs start with connector, wiring, power, and ground checks before replacing any parts.
  • Intermittent faults are common; live-data logging and a harness wiggle test can be critical to reproduce the issue.
  • Because braking and stability functions may rely on this signal, treat the code as potentially safety-relevant.
  • Verify pinouts, routing, and test steps with service information because monitoring logic varies by vehicle.

Vehicles Commonly Affected by P0555

  • Vehicles equipped with an electronically monitored brake booster pressure sensor as part of the powertrain control strategy
  • Vehicles using brake booster pressure data for idle control, torque management, or drivability coordination
  • Vehicles with integrated stability/traction functions that share brake-related signals across modules
  • Vehicles frequently driven in high-humidity, high-salt, or heavy rain environments where connector corrosion is more likely
  • Vehicles with prior collision repair or underhood service that may disturb harness routing or connector engagement
  • Vehicles with aging engine-bay wiring insulation or heat exposure near exhaust components
  • Vehicles that experience rodent damage or abrasion at harness contact points
  • Vehicles with intermittent electrical issues related to loose grounds or poor terminal tension

FAQ

Does P0555 mean the brake booster is bad?

No. P0555 indicates a detected fault in the brake booster pressure sensor circuit. The code alone does not confirm a failed brake booster or a specific mechanical problem; it points to an electrical/signal issue that must be verified with testing.

What is the first thing to check for P0555?

Start with a visual and hands-on inspection of the sensor connector and harness: look for corrosion, moisture, loose pin fit, damaged insulation, and harness contact with sharp edges or hot components. Then confirm power supply and ground integrity to the circuit using the correct test procedures for your vehicle.

Can a loose connector cause P0555 intermittently?

Yes. Poor terminal tension, partial connector engagement, or fretting corrosion can create intermittent opens or high resistance that come and go with vibration or temperature changes. A wiggle test combined with live-data logging is often useful to confirm this type of fault.

Should I replace the brake booster pressure sensor right away?

Not until circuit checks are completed. Many P0555 cases are caused by wiring, connector, power, or ground issues. Replace the sensor only after confirming the circuit is intact and the fault follows the sensor per the diagnostic steps in service information.

Will clearing P0555 fix the problem?

Clearing the code only resets the stored fault information; it does not correct the underlying circuit problem. If the fault is still present, the monitor will typically set P0555 again when the enabling conditions are met and the diagnostic runs.

For a lasting repair, confirm the exact circuit fault with testing, correct the verified cause, and then clear the code and perform a recheck so the monitor can complete without returning P0555.