P0557 on 2017-2020 Buick Envision (Preferred, Essence, Premium, Premium II) — Brake Booster Pressure Sensor Circuit Low
1 vehicles · 1 makes · $300-$950 repair
How to diagnose and fix P0557: most-reported vehicles
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Buick Envision · 2017–2020
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
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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?
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.
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?
Repair costs for P0557 range from $300 to $950, depending on the vehicle and root cause.
Which vehicles are affected by P0557?
Au7o has documented P0557 across 1 vehicle models from 1 manufacturers: Buick.
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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.