P0557 on Buick: How to Diagnose & Fix
Brake Booster Pressure Sensor Circuit Low
1 Buick model · 1 documented issue · 1 critical · $300-$950 repair
P0557 on Buick by model: symptoms, diagnosis and fix
Owners report a 'Service Brake Assist' message appearing while driving, immediately followed by a brake pedal that is either rock-hard and requires extreme force, or that goes unresponsive and then sinks to the floor when pumped. Two NHTSA complaints on the 2019 describe this at only about 4,300-4,700 miles. GM TSB 21-NA-107 covers 'Service Brake Assist' messages with the Service Engine Soon lamp and DTC P0557 stored, and attributes them to inconsistent in-rush current on the brake booster vacuum sensor's 5V reference during stop/start crank events.
Common Symptoms
- 'Service Brake Assist' message on the driver information center
- Brake pedal extremely hard, requiring heavy force to stop
- Pedal sinks to the floor after pumping
- Service Engine Soon lamp illuminates after the brake message clears
How to Fix
Scan for P0557 and follow GM TSB 21-NA-107, which replaces the power brake booster vacuum pipe with a later version containing a more robust sensor (Envision 2.5L LCV part 84974396, about 0.3 hr labor, covered under bumper-to-bumper warranty terms), then clears the codes. Treat any pedal-to-floor event as an unsafe condition and stop driving the vehicle until diagnosed.
Sources for this issue (4)
- 2019 Buick Envision - Service 'Brake Assist' Light And Brake Failure (NHTSA complaints at ~4,300 and ~4,700 miles)article
- 2019 Buick Envision TSBs - 21NA107 Service Engine Soon lamp with brake assist messagetsb
- 2018 Buick Envision TSBs - 21NA107 service brake assist message with DTC P0557 storedtsb
- GM Service Bulletin 21-NA-107 (NHTSA copy)tsb
P0557 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0557 mean on a Buick?
P0557 stands for "Brake Booster Pressure Sensor Circuit Low." The PCM detects voltage on the brake booster pressure sensor circuit that is lower than expected (short to ground or open). The booster pressure input is invalid. On Buick it is documented across 1 model: Envision.
What are the most common causes of P0557?
The most common causes of P0557 are: Short to ground in sensor wiring, Open circuit in the sensor circuit, Failed brake booster pressure sensor, Corroded/loose connector. The specific cause varies by vehicle.
How much does it cost to fix P0557 on a Buick?
Published repair estimates on Buick range from $300 to $950 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.