Failed brake booster pressure sensor; Damaged, corroded, or disconnected electrical connector at the sensor; Open or shorted wire in the sensor signal circuit; Poor ground connection for the sensor or PCM; Vacuum leak at the brake booster, check valve, or hose causing incorrect pressure readings; Faulty powertrain control module (PCM) or body control module (BCM), though rare

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0557

P0557Brake Booster Pressure Sensor Circuit Low Input

Q: What does code P0557 mean?

Brake Booster Pressure Sensor Circuit Low Input. P0557 means the powertrain control module (PCM) has detected a low input voltage from the brake booster pressure sensor circuit, which monitors the vacuum or hydraulic pressure assisting your brakes. The sensor signal is below the expected range, so the PCM cannot reliably determine brake booster pressure and sets this code.

P0557 means the powertrain control module (PCM) has detected a low input voltage from the brake booster pressure sensor circuit, which monitors the vacuum or hydraulic pressure assisting your brakes. The sensor signal is below the expected range, so the PCM cannot reliably determine brake booster pressure and sets this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
A hard or stiff brake pedal that requires extra effort to stop the vehicle
Reduced braking assist, especially during the first few presses after starting the engine
A hissing noise from the brake booster area when the brake pedal is pressed
An intermittent or flickering brake warning light in some vehicles
Poor engine idle quality if the booster has a vacuum leak that affects engine vacuum

Common causes, most likely first

Failed brake booster pressure sensor
Damaged, corroded, or disconnected electrical connector at the sensor
Open or shorted wire in the sensor signal circuit
Poor ground connection for the sensor or PCM
Vacuum leak at the brake booster, check valve, or hose causing incorrect pressure readings
Faulty powertrain control module (PCM) or body control module (BCM), though rare

How to diagnose and fix it

Inspect the brake booster pressure sensor connector and wiring for corrosion, damage, or loose pins
Check the sensor's reference voltage and ground circuits with a digital multimeter
Test the sensor signal voltage and compare it to the manufacturer's specification while applying the brake pedal
Inspect the brake booster vacuum hose, check valve, and booster body for leaks or cracks
Replace the brake booster pressure sensor if testing confirms it is faulty
Repair or replace damaged wiring or connectors as needed
Clear the diagnostic trouble codes and verify the repair with a test drive

Don't overlook the vacuum system

A vacuum leak at the brake booster can cause the sensor to read low pressure even when the sensor itself is good, so always check the booster and hoses before replacing parts.
The brake booster pressure sensor is sometimes integrated into the brake booster assembly, making replacement more involved and costly than a standalone sensor.
A low input code can be set by a poor ground connection at the sensor or PCM, which is often overlooked during diagnosis.
In some vehicles, a failing brake booster check valve can cause intermittent low pressure readings that only appear during certain driving conditions.
This code does not always mean the sensor is bad; wiring issues and vacuum leaks are common culprits that should be ruled out first.

Can I keep driving with P0557?

If the brake pedal feels normal, you can drive cautiously to a repair shop, but avoid heavy braking or towing. If the pedal is hard or braking assist is reduced, stop driving and have the vehicle towed to prevent an accident.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.