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P0556 OBD-II Trouble Code: Brake Booster Pressure Sensor Circuit Range/Performance

check engine light

P0556 code definition

The P0556 code gets stored when the PCM has detected a problem with the brake booster pressure sensor circuit because of abnormal feedback.

What the P0556 code means

When you’re slowing down, if your vehicle’s PCM doesn’t receive a voltage input from its brake booster pressure sensor that is in proportion to the decrease in speed, the P0556 will be stored and the Check Engine Light will come on.

As such, this code usually occurs when you’re applying the brakes. However, some vehicles actually require numerous ignition cycles with the code being triggered before it will go ahead and turn on the Check Engine Light. Still, the code should be stored by the PCM since the initial incident.

What causes the P0556 code?

More often than not, the P0556 code is stored because of a malfunctioning brake booster pressure sensor or leaks between the vacuum and the vacuum brake booster. Other common reasons include:

What are the symptoms of the P0556 code?

In some rare cases, you may not notice any symptoms at all. Even the Check Engine Light may not come on. Typically, though, you’ll probably notice your brake pedal requires more pressure to compress. This is a problem that will most likely get worse as time goes on.

How does a mechanic diagnose the P0556 code?

Your mechanic will use a brake booster pressure sensor to assess how much braking assist pressure is present for bringing your vehicle to a halt. Other tools your mechanic will most likely need include an OBD-II scanner and a digital ohmmeter. They’ll still do a visual assessment of all connectors and wires too. The brake booster system will be looked over. After each component they check on, the mechanic will retest the system to see if there is a change in the codes stored. The mechanic will do a test drive as well.

Common mistakes when diagnosing the P0556 code

As we mentioned above, this code may be triggered because hydraulic brake boosters fail. However, the reason behind that is usually because power steering malfunctions. In that case, low power steering fluid is typically responsible. It’s important to understand this relationship or a mechanic may carry out a miscellaneous repair process but the problem will persist.

How serious is the P0556 code?

You should never take chances where your vehicle’s brakes are concerned. Even if it’s just slightly harder to compress them right now, that could easily lead to some kind of accident. Also, at the moment, you may not mind having to put a little extra effort forward to slow your vehicle, but it could get progressively worse and eventually surprise you, which would be extremely dangerous.

What repairs can fix the P0556 code?

Common steps mechanics take to repair the problems associated with the P0556 code are:

Additional comments for consideration regarding the P0556 code

If your vehicle uses a hydraulic booster, the mechanic will need to inspect it. To find out if the sensor is the thing causing the problem, use the power brake booster sensor connector and use the digital ohmmeter to check sensor resistance. Then, compare the finding with your vehicle’s manufacturer’s specifications. If the readings don’t coincide, you should get rid of the faulty sensor.

Need help with a P0556 code?

If your vehicle is suffering from any of the above symptoms, YourMechanic is here to help. Just call 1-800-701-6230 to speak with one of our service advisors or you can fill out an online form. Either way, we’ll learn about your problem, provide you with a quote and then send a certified mobile mechanic to your home or place of work to diagnose your vehicle and carry out necessary repairs right away.

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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