Some owners of 2018-2021 GMC Terrain vehicles equipped with an LTG or LYX engine may comment on a Service Brake Assist message.
DTC P0557 may be found stored. The cause may be inconsistent in-rush current provided by the 5V reference during the start/stop crank event.
Replace the power brake booster vacuum pipe with the later version, containing a sensor that is more robust against in-rush variation during the start/stop crank events.
The correct part number for LTG engines is 84974393. The part number for LYX engines is 84974392.
