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P0556 Brake Booster Pressure Sensor Circuit Range

OBD-II Trouble Code Technical Description

Article by
John Ingalls
John Ingalls
Former Service Manager & Air Force Mechanic

Brake Booster Pressure Sensor Circuit Range/Performance

What does that mean?

This is a generic powertrain diagnostic trouble code (DTC) and applies to OBD-II vehicles that have a brake booster pressure sensor. That may include but is not limited to vehicles from Fiat, Alfa Romeo, Nissan, Ford, Dodge, Pontiac, Chevrolet, Acura, Subaru, Hyundai, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.

Trouble code P0556 is one of several possible codes associated to the Brake Booster Pressure Sensor Circuit.

This code is an indication that the Powertrain Control Module (PCM) has detected a malfunction that is hindering the operation of the brake booster pressure sensor circuit. The codes that are commonly associated to brake booster pressure sensor circuit malfunctions are P0555, P0556, P0557, P0558 and P0559. The specific situation determines the code activated by the PCM and the brake warning light will be illuminated or flash when braking.

The purpose of the brake booster pressure sensor circuit is to monitor the amount of pressure (vacuum) applied to the power brake booster. The circuit is controlled by the PCM to adapt various braking situations and adjust the pressure to assist brake pedal operation. This process is essential for the power brakes to function properly and safely slow down or stop the vehicle with the minimum amount of foot pressure being applied to the brake pedal.

Code P0556 is set by the PCM when the brake booster pressure sensor circuit is out of range or not performing properly.

What is the severity of this DTC?

The severity of this code varies based on the specific malfunction and the severity level will progress if not corrected in a timely manner. At some point the safety level of the vehicle could become an issue requiring immediate attention.

Photo of a brake booster pressure (vacuum) sensor:
P0556 Brake Booster Pressure Sensor

What are some of the symptoms of the code?

Symptoms of a P0556 trouble code may include:

What are some of the common causes of the code?

Causes for this P0556 code may include:

What are some P0556 troubleshooting steps?

The first step in the troubleshooting process for any malfunction is to research the Technical Service Bulletins for known issues with the specific vehicle.

Locate all of the components associated with the Brake Booster Pressure Sensor Circuit. This will include the brake booster pressure sensor, the brake booster, vacuum lines, wiring, connectors and the PCM on a simplex system. Once these components are located, a thorough visual inspection should be conducted to check all of the associated wiring and connectors for obvious defects such as scraping, rubbing, bare wires or burn spots. The connectors should also be examined for corrosion build up or damaged pins. Vacuum lines should be inspected for security, weather cracks, leaks and the overall serviceability level.

Advanced Steps

The advanced steps become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multi meter and the specific technical references for the vehicle. Voltage requirements will very based of the specific year, make and model of the vehicle.

Circuit Checks

Voltage requirements will vary based on the specific vehicle, the Brake Booster Pressure Sensor Circuit configuration and the components incorporated. Tech data should be referenced to obtain the correct voltage range for the Brake Booster Pressure Sensor and the appropriate trouble shooting sequence. The correct voltage input to a sensor with no output voltage is normally an indication of internal failure.

If this process identifies the absence of a power source or ground, continuity testing may be needed to check the condition of the wiring and connectors. Continuity tests are always performed with the power removed from the circuit and the normal readings should be 0 ohms of resistance unless otherwise specified by the technical data. Resistance or no continuity is an indication of faulty wiring or connectors that are shorted or open and must be repaired or replaced.

Common Repairs

Hopefully, the information in this article has been helpful to point you in the right direction to correct the problem with your brake booster pressure sensor trouble code. This article is strictly informational and the specific technical data and service bulletins for your vehicle should always take precedence.

Related P0556 DTC Discussions

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