The owner of a 2013-14 Buick Encore SUV may come into your store with a complaint that his brake pedal feels very low or sinks to the floor on brake application.
On investigation, you may find trouble code C027B stored in the ABS control module. One likely cause for both conditions is a small vacuum leak between the master cylinder and brake booster. A missing or dislodged O-ring is the cause of the leakage.
The illustration shows a typical Buick Encore master cylinder/brake booster setup. The O-ring should fit over the raised area on the cylinder and into a small groove in the booster, as shown.
What could cause the O-ring to dislodge or go missing? This typically occurs when the master cylinder is disconnected and positioned aside to get to another component for repair. Repositioning or installing a new O-ring should eliminate the vacuum leak and subsequent brake pedal issues.