Technical Description of OBD-II Trouble Code
The circuit range/performance of the brake booster pressure sensor is being detected.
What does that mean?
This is a generic diagnostic trouble code (DTC) for powertrain and applies to OBD-II vehicles equipped with a brake booster pressure sensor. This includes vehicles from various manufacturers such as Fiat, Alfa Romeo, Nissan, Ford, Dodge, Pontiac, Chevrolet, Acura, Subaru, Hyundai, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration of the vehicle.
Trouble code P0556 is one of several codes associated with the brake booster pressure sensor circuit.
This code indicates that the Powertrain Control Module (PCM) has detected a malfunction that is affecting the operation of the brake booster pressure sensor circuit. The codes commonly associated with brake booster pressure sensor circuit malfunctions are P0555, P0556, P0557, P0558, and P0559. The specific code activated by the PCM and the brake warning light will illuminate or flash when braking, depending on the situation.
The purpose of the brake booster pressure sensor circuit is to monitor the amount of pressure (vacuum) applied to the power brake booster. The PCM controls the circuit to adapt to different braking situations and adjust the pressure to assist in brake pedal operation. This process is crucial for the proper functioning of power brakes and for safely slowing down or stopping the vehicle with minimal foot pressure on the brake pedal.
Code P0556 is set by the PCM when the brake booster pressure sensor circuit is out of range or not functioning properly.
What is the severity of this DTC?
The severity of this code varies depending on the specific malfunction, and if not corrected in a timely manner, the severity level will increase. At some point, the safety of the vehicle could be compromised, requiring immediate attention.
Photo of a brake booster pressure (vacuum) 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 buildup or damaged pins. Vacuum lines should be inspected for security, weather cracks, leaks, and overall serviceability.
Advanced Steps
The advanced steps become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multimeter and the specific technical references for the vehicle. Voltage requirements will vary based on 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 incorporated components. Tech data should be referenced to obtain the correct voltage range for the Brake Booster Pressure Sensor and the appropriate troubleshooting 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 in pointing 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.
