P0557 code definition
The P0577 vehicle trouble code indicates an issue with the brake booster pressure sensor circuit.
What the P0557 code means
The P0577 code identifies a pressure problem within the brake booster. When the brake booster pressure sensor fails to send a voltage input signal to the PCM that is satisfactory (or proportionate to the vehicle velocity required) the P0557 code will be stored. This usually indicates that the brakes were applied and the pressure within the brake system was not sufficiently to factory specifications.
Some vehicles will require multiple ignition cycles in which this problem occurs to trigger the check engine indicator light, but the P0557 code will still be stored, sometimes as a “pending code” if the issue is only an initial failure.
What causes the P0557 code?
The P0557 code has a number of common causes:
- An issue with the brake booster pressure sensor
- Vacuum leaks into the vacuum brake booster
- Defective or broken vacuum hoses
- Defective or broken electrical circuitry
If your vehicle’s brake boosters are hydraulic:
- Issues with power steering malfunctions
- Low power steering fluid
- Low hydraulic brake booster pressure
- Issues with the power steering pump
What are the symptoms of the P0557 code?
When the P0557 code appears, it is usually accompanied by the Check Engine light illuminating on the vehicle’s dashboard. Depending on the source of the problem, physical symptoms of a brake issue may be present before the Check Engine light illuminates. The brake pedal may be unresponsive or softer than usual. Brake performance may be affected. In some cases, brake performance is not affected but the feel of the brake pedal is still noticeably softer. It may take multiple presses of the brake pedal to cause the OBD-II system to store the P0557 code.
How does a mechanic diagnose the P0557 code?
A qualified technician with an OBD-II code scanner capable of retrieving factory readings from the vehicle. The technician will view the trouble code and see the time that it was stored. After that has been observed, the codes will be cleared before the vehicle is taken for a test drive. If, during the course of the drive, the code appears again, then it will be confirmed that the problem is indeed related to the P0557 code and not an intermittent issue that may be caused by electrical malfunctions.
Once the P0557 code is confirmed as the source of the problem, then the diagnosis can move onto the next step. The technician will use a voltmeter to test the circuits around the brake booster pressure sensor and the powertrain control module. A visual inspection of the wires and connections will then take place. After that, the inspection will move onto the brake booster itself and all of the vacuum lines surrounding it.
Common mistakes when diagnosing the P0557 code
While a malfunctioning brake booster will cause the P0557 code to appear, the code can also be caused by an electrical malfunction or a leaking vacuum line. In applications that use a hydraulic brake booster, leaking hydraulic fluid lines and leaky connections can cause the P0557 code to appear. The sensor responsible for monitoring pressure within the brake booster is prone to malfunctioning as well. If this sensor cannot properly read and relay that data, the P0557 code will appear.
How serious is the P0557 code?
The P0557 code is serious enough to warrant getting a professional to diagnose the problem as soon as the code appears. A problem with the brakes is inherently hazardous, and declining brake performance is dangerously unpredictable. The code itself will not prevent the engine from starting, but that does not mean that the vehicle is safe to drive when the brake booster does not have proper pressure.
What repairs can fix the P0557 code?
The most common repairs to address the P0557 code are as follows:
- Brake booster repair or replacement
- Brake booster pressure sensor replacement
- Replace faulty vacuum lines in brake system
- Replace faulty hydraulic lines in brake system
- Replace or adjust connections within the lines of the braking system
- Repair or replace circuitry surrounding the brake booster pressure sensor
- Repair or replace faulty powertrain control module
Additional comments for consideration regarding the P0557 code
Do not replace parts such as the brake booster prior to having the P0557 code diagnosed by a qualified technician. Often the problem is rooted in an electrical malfunction or a leaking vacuum line within the brake system.
Need help with a P0557 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.
This article originally appeared on YourMechanic.com as P0557 OBD-II Trouble Code: Brake Booster Pressure Sensor Circuit Low and was authored by Ian Swan.