Error Code P0555 is defined as Brake Booster Pressure Sensor Circuit. This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-system and brake booster pressure sensor. It’s particularly common, but not limited to Acura, Alfa Romeo, Chevrolet, Dodge, Ford, Hyundai, Nissan, Pontiac, Subaru, etc. Though generic, specifications on the definition, troubleshooting, and repairs may vary with the year, make, model, and powertrain configurations of the vehicle.

The job of the brake booster pressure sensor circuit is to monitor the amount of pressure (vacuum) applied to the power brake booster. This process is controlled by the PCM to allow the vehicle to adapt to various braking situations and adjust the pressure needed by the vehicle to assist the operation of the brake pedal. This process is crucial for the power brakes to work efficiently and safely, and safely slow down or stop the vehicle with a minimum amount of foot pressure being applied to the vehicle.

Error Code P0555 is one of the many possible codes associated with the brake booster pressure sensor circuit. When this appears, it means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has determined an error that hinders the performance of the brake booster pressure sensor circuit.

Specific situations determine the code which the PCM activates. Other related brake booster pressure sensor circuit error codes include:

Common Symptoms

When this code appears, it will illuminate the Check Engine light, or flash it when braking. Other common symptoms include:

  • Check brake light flashes or stays illuminated
  • Pressing the brake pedal requires increased effort

Possible Causes

  • Faulty brake booster pressure sensor
  • Damaged or worn vacuum lines
  • Faulty wiring
  • Corroded or damaged connector
  • Defective brake booster
  • Defective PCM

How to Check

As with most trouble codes, it is best to refer with your TSB (Technical Service Bulletin) when troubleshooting this code.

Start by locating all components related to the Brake Booster Pressure Sensor Circuit. This includes the sensor itself, the brake booster, vacuum lines, wirings, and connectors to the PCM. As soon as you find these components, inspect the connectors and wirings for signs of damages, such as scraping, bare wires, burn spots, rubbing, etc. Also, check the connectors for signs of corrosions buildup, or damaged pins. Vacuum lines must be checked for weather cracks, leaks, and overall serviceability level.

Advanced Steps

Next step for diagnosis is usually vehicle specific and may require the appropriate and advanced equipment to be conducted properly. This includes the use of a digital multimeter, and specific technical references for the vehicle, as with the voltage requirement, is usually based on the make, model, and specific year of the vehicle.

Circuit Checks

As said earlier, voltage requirement vary for the specific vehicle, the configuration of the brake booster pressure sensor circuit, and all components incorporated into the system. Thus, tech data must be referenced to obtain the right voltage range from the brake booster pressure sensor and the appropriate troubleshooting sequence.

The correct voltage input to a sensor without output voltage is usually a sign of internal failure.

If this process confirms the absence of power source or ground, then you should conduct a continuity test to check the condition of the connectors and wirings. This test is always performed with power removed from the circuit, while normal readings should start at 0 ohms of resistance unless otherwise specified by the technical data from the TSB.

Resistance or no continuity means there’s a faulty wiring or connector issue that is shorted or open, which must be repaired, if not replaced.

How to Fix

Depending on your diagnosis, common repairs for this code include:

  • Replacement of faulty brake booster pressure sensor
  • Cleaning corrosion from connectors
  • Repair or replacement of faulty wiring
  • Replacement of brake booster
  • Replacement of PCM (rare)


Severity for this problem depends on the specific malfunction. Usually, though, this condition progress over time if not corrected, which could pose a safety risk. Thus, this code requires immediate attention.