This bulletin applies to 2012-2013 Buick Regal and LaCrosse vehicles with eAssist. A hum or buzz noise may be heard from the right front service brake when driving straight or when turning, along with a Service Brake Assist message displayed, and DTCs C027B or C0040.
The forward lamp harness may be contacting the crank pulley, air conditioning compressor pulley or accessory drive belt due to misrouting or improper installation.
Repair the wiring as needed or replace the forward lamp harness, correct routing and properly secure all driven components. Once wiring repairs are complete, confirm proper brake booster vacuum pump operation. The pump can be commanded-on using GDS2.