P0559Generic code

P0559 Code: Brake Booster Pressure Sensor Circuit Intermittent

The P0559 code means the brake booster pressure sensor signal cuts out or jumps from time to time. The main risk is a possible loss of brake assist. Intermittent faults are almost always a poor contact or a damaged wire, so you have to reproduce the problem to find it.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$40 to $300
Difficulty
Medium
System
Chassis, Brakes and Suspension
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0559 code means

On vehicles with an electric vacuum pump, or with engines that make little vacuum (direct injection, turbo, hybrids), a sensor measures the brake booster vacuum so the pump can be turned on or the engine adjusted.

The sensor gets a 5 V reference and a ground from the computer and returns a signal between about 0.5 and 4.5 V. Intermittent dropouts, which are what the P0559 code reports, almost always come from a poor contact or a damaged wire.

Without a steady signal, the computer does not know whether there is enough brake assist. It may run the vacuum pump continuously or turn on a brake warning. Always check that the brake pedal has normal assist.

Intermittent faults are found by reproducing them. With the engine running and the scan tool in graph mode, move the wiring harness section by section, tap the connector gently and, if needed, warm the area with a hair dryer or wet the connector with a spray bottle. The spot where the reading jumps is where the fault is.

P0559 code symptoms

  • Check engine light on.
  • Possible loss of brake assist.
  • Hard brake pedal.
  • Vacuum pump running continuously.
  • Brake warning.

Likely causes of the P0559 code

  1. Poor contact in the connector. Loose or backed-out pins.
  2. Wire broken inside its insulation. It opens the circuit with vibration.
  3. Harness rubbing against moving or hot parts.
  4. Sensor with an intermittent fault, often depending on temperature.

How to diagnose the P0559 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check the supply and ground with the key on: the reference should be correct, with less than 0.1 V of voltage drop on the ground.
  4. Measure the signal with the connector plugged in and watch whether it changes with the condition.
  5. Do a wiggle test on the harness with the scan tool in graph mode.
  6. Check the continuity of each wire to the computer (under 1 ohm).

How to fix the P0559 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is bad.
  • Correct the real condition if there is one.
  • Clear the codes and verify with a road test.

Technical reference data

  • 5 V reference, ground and a signal proportional to the vacuum.
  • These values are a general guide: check the manufacturer data for your vehicle.

Brand-specific notes

This code is usual on vehicles that rely on an electric vacuum pump or that make little engine vacuum.

P0559 on BMW

Usual on BMW vehicles.

P0559 on Volkswagen

Usual on Volkswagen vehicles.

P0559 on Ford EcoBoost

Usual on Ford EcoBoost engines.

P0559 on Hybrids

Usual on hybrid vehicles.

Frequently asked questions about P0559

Can I drive with a P0559 code?
With great caution. If the brake pedal is hard, stopping takes more force, so have it checked as soon as you can.
What does the P0559 code mean?
It is a generic OBD2 code that means the brake booster pressure sensor signal cuts out or jumps from time to time. The result can be a loss of brake assist.
Do I have to replace the sensor?
Only if the tests confirm it. The connector and the wiring fail just as often.
What does the brake booster pressure sensor do?
On vehicles with an electric vacuum pump, or with engines that make little vacuum (direct injection, turbo, hybrids), a sensor measures the brake booster vacuum so the pump can be turned on or the engine adjusted.
How much does it cost to fix P0559?
As a rough guide, between $40 and $300. A connector or wiring repair is at the low end, and a new sensor with labor is at the high end.
Will a P0559 code clear itself?
The light may go out if the fault stays away for several drive cycles, but an intermittent P0559 code usually returns. Find the poor contact instead of waiting for it.
What is the most common cause of P0559?
A poor contact in the connector, such as loose or backed-out pins. A wire broken inside its insulation and a harness rubbing on a moving part come next.

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