P0556 - OBD Trouble Code

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P0556 is a diagnostic trouble code (DTC) for "Brake Booster Pressure Sensor Circuit Range/Performance". This is a generic powertrain diagnostic trouble code (DTC) and applies to OBD-II vehicles that have a brake booster pressure sensor. This code is set when PCM fails to receive a voltage input signal from the brake booster pressure sensor that is proportionate to the decrease in vehicle speed required, a code will be stored and a malfunction indicator lamp will be illuminated.

OBD-II Code Powertrain Control Module (PCM) failure is defined as a Brake Booster Pressure Sensor Circuit Range/Performance. It indicates that PCM has detected a fault in the brake booster pressure sensor circuit. Brake booster pressure sensor is connected to brake booster by a hose. It detects brake booster pressure and sends the voltage signal to the Engine Control Module (ECM). 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. This problem normally occurs when the brakes are applied.

If the ECM/PCM detects an improbable signal from the Brake Booster Pressure Sensor, code P0556 will be set.

What causes this problem with the Brake Booster Pressure Sensor Circuit Range/Performance?

• Damaged or broken vacuum lines or hoses
• Faulty brake booster
• Defective or faulty wiring
• Damaged, broken or corroded connector
• Faulty brake booster pressure sensor
• ECM issue

1. Brake Booster - The brake booster improves braking performance and safety by reducing the pedal pressure. Replace or repair the faulty one to avoid any major issue.
2. Brake Connector - Check out the brake connector on regular basis as the corroded or broken connector could also be the cause for storing this code.
3. Brake Pedal - If you face any difficulty while compressing the brake pedal then kindly repair or replace it as it could lead to the accidents as well.
4. Vacuum Hose - Leaked vacuum hoses or lines can create major issues in no time so always repair or replace the leaked vacuum hoses immediately.
5. ECM/PCM - The Engine Control Module (also called the Powertrain Control Module or PCM) is the brains of the engine management system. It controls the fuel mixture, ignition timing, variable cam timing and emissions control.

Please note that it may take a while before your service engine light comes on, so it is important to recognize these other symptoms ahead of time. Knowing these symptoms will help you fix it quickly.

• Extra pressure required to compress brake pedal
• Illuminated check brake light
• Flashed brake light while braking
• Illuminated check engine light

It is very important to resolve this error code on time as it is connected with brakes. Due to this error code you might face difficulty in compressing brake pedal which can lead to the accident as well. Initially you may not find it much difficult but if ignored it could become progressively worse and ultimately extremely dangerous. To fix this code following repairs and replacements may help:

• Check all the electrical connections carefully and repair or replace the faulty one as required.
• Replace the faulty brake booster pressure sensor.
• Repair or replace the leaked vacuum lines or hoses.
• Inspect the brake booster; replace it if you discover it faulty.
• Clean the corrosion from connectors.

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This diagnostic trouble code (DTC) is a generic powertrain code. Although generic, the specific repair steps may vary depending on make/model. Some basic steps to diagnose this code are as follows:

• Begin with a visual inspection of all wiring and connectors.
• Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary.
• Continue by clearing the code and operating the vehicle to see if it returns.
• Proceed with your diagnosis with a visual inspection of the brake booster system.
• Make sure that there is no fluid leaking from the rear of the master cylinder into vacuum booster.
• Inspect all vacuum supply hoses used to supply the vacuum brake booster.
• If the system uses a hydraulic booster, visually inspect the power steering pump, lines, fluid condition, and fluid level.
• Also take a look at the pressure sensor, as well as the electrical wiring and connectors for signs of damage from corrosion, burning, or fluid contamination.
• Repair or replace faulty components as required. If the vacuum source checks out and no wiring or connectors are damaged, then connect the scanner (or code reader) and make a note of all stored codes and relevant freeze frame data.
• Test drive the vehicle and see if the code persists; if it does, then proceed with the diagnostic strategy. Disconnect the power brake booster sensor connector and check sensor resistance using the digital volt/ohmmeter.
• Compare your findings with manufacturer’s specifications and dispose of the sensor if actual readings do not coincide.
• If the sensor checks out, test the sensor connector for voltage and ground signals.
• If no voltage and ground signals are detected, disconnect the PCM connector and perform a continuity test on the entire circuit in order to isolate a possible malfunction and repair open or shorted wiring as required.
• If voltage and ground signals are present, connect the manual power steering pressure gauge or vacuum gauge.
• Consult your vehicle’s service manual and compare your findings, replace or repair power steering system or vacuum supply/engine components as needed.

Common Mistakes When Diagnosing the P0556 Code

As the description of this code suggests that this code is related to the brake booster pressure sensor so believing that the faulty sensor is the main cause responsible for storing this code is the biggest mistake usually people do while diagnosing this code and they replace the sensor instead of doing a thorough diagnosis.