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P0559 OBD-II Trouble Code: Brake Booster Pressure Sensor Circuit Intermittent

check engine light

P0559 code definition

The P0559 trouble code detects an issue with the brake booster pressure sensor circuit.

What the P0559 code means

The P0559 code is a generic OBD-II trouble code that signifies a problem with the brake booster pressure sensor. The vehicle relies on the brake booster pressure system to aid braking, and the pressure sensor sends voltage input signal readings to the powertrain control module (PCM). When the voltage input signals do not match the rate of deceleration for the vehicle, then the P0559 code will be detected.

What causes the P0559 code?

Some potential causes of the P0559 code include:

  • Vacuum leak in the vacuum brake booster
  • Malfunctioning brake booster pressure sensor
  • Broken or damaged brake booster vacuum hoses
  • Damaged valve in the vacuum brake booster supply hose
  • Loose, corroded, or damaged electrical components or circuits
  • Low power steering fluid or malfunctioning power steering pump (which leads to hydraulic brake booster failure)
  • In rare cases, a defective brake booster

What are the symptoms of the P0559 code?

The P0559 trouble code will usually be accompanied by the check engine soon Warning Light illuminating on the instrument cluster. Usually the brake pedal will become harder and more resistant, though it is possible for there to be no noticeable drivability symptoms.

How does a mechanic diagnose the P0559 code?

The P0559 code should be diagnosed using a standard OBD-II trouble code scanner. A trained mechanic can use the scanner to look at the freeze frame data to assess the code, and to look for any additional trouble codes that may be present. The codes should then be reset, and the vehicle restarted. If the trouble code does not return, it was likely stored erroneously, or it may be an intermittent issue.

If the P0449 trouble code remains on, then the technician should visually inspect the brake booster electrical components. All wires and connectors should be inspected, and any that are loose, corroded, or damaged should be replaced. In addition to the wires, the power steering fluid levels should be checked.

Next, the mechanic will inspect the brake booster system, and will check the sensors, hoses, and valves, to see if any defective components can be spotted. All defective components should be replaced, not repaired.

Each time a something is found and replaced, the codes should be reset, and the vehicle restarted. That way the mechanic will know exactly when the issue has been resolved. Once the code has gone away, the technician should take the vehicle for a short test drive to make sure that the brakes feel normal.

Common mistakes when diagnosing the P0559 code

The most common mistake made when diagnosing the P0559 trouble code comes from not properly following the OBD-II trouble code diagnosis protocol. It is imperative that mechanics follow the protocol step by step, to ensure an efficient and thorough inspection and repair.

Brake boosters are frequently replaced when the P0559 trouble code is detected. However, total brake booster failure is very uncommon, and usually the issue is merely a single component within the system.

How serious is the P0559 code?

A vehicle with a detected P0559 code is still drivable. However, the brakes will likely be harder to deploy, which can make driving more dangerous, and the brake system may not work as efficiently and effectively as possible. As brakes are the most important safety feature in a vehicle, the P0559 code should be addressed immediately.

What repairs can fix the P0559 code?

Some of the repairs for the P0559 code are:

Additional comments for consideration regarding the P0559 code

In some vehicles, the P0559 will only be detected when the issue has happened during multiple ignition cycles. If this is the case, then it may appear as a “pending code” after the first instance.

Need help with a P0559 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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