P0556: How to Diagnose & Fix — Brake Booster Pressure Sensor Circuit Range/Performance

The T1 generation Silverado can experience brake assist malfunctions, causing a hard brake pedal, longer stopping distances, and warning lights. The electric brake booster or its sensors may be the cause.

The vacuum pump that provides brake assist on EcoBoost F-150s can fail, resulting in a hard brake pedal and reduced braking assist. Since turbo engines don't produce intake vacuum like naturally aspirated engines, they rely on this pump.

NHTSA recall 21V890/Toyota 21TA09 covers certain non-hybrid 2018-2019 Camrys with the A25A-FKS engine, not Camry Hybrids or every vehicle in those model years. An affected vacuum-pump vane end cap can wear, break and lodge between the vane and housing, stopping the pump and suddenly reducing brake assist. The service brakes still function, but pedal effort increases and braking performance may be reduced, increasing crash risk. Toyota reports no expected advance warning before the condition occurs.

Third-generation Equinox (2018-2022) uses a camshaft-driven mechanical vacuum pump mounted at the rear of the cylinder head to supply the brake booster (the turbo intake is pressurized, so there is no manifold vacuum). This pump can seize and its drive gear break, suddenly eliminating brake assist — the pedal becomes 'hard as a rock' with greatly increased stopping distances. In severe cases the pump shatters and sends metal debris into the engine, causing catastrophic internal damage. NHTSA has over 300 complaints; a related GM recall (19V645000) reprogrammed the brake control module on other models but excluded the Equinox/Terrain, and a February 2026 class action (Thieme v. General Motors) targets 2018-2022 Equinox/Terrain.

GMC Yukons from 2015 through 2018 fall under NHTSA recall 19V645000. The defect: the amount of vacuum created by the vacuum pump may decrease over time. Less vacuum reaching the brake booster means less brake assist, so the Yukon's pedal grows stiff and the truck's stopping distance stretches out - NHTSA flags this as raising the risk of a crash. Worth distinguishing from an outright vacuum pump failure: this recall is about assist that tapers off as pump output declines, and GM's approved correction is a control-module calibration rather than a pump replacement. The 3,456,719-vehicle figure attached to this campaign is the total across every GM model included in it.