C0021Brake Booster Performance
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- A performance code for the power brake booster, set when the booster does not deliver the expected level of assist or does not respond to the control module as commanded. On vehicles with an electronic or vacuum booster the module compares driver pedal demand, measured boost and the resulting brake pressure, and stores the code when assist is weak, slow or inconsistent. GM documents C0021 setting on 2019-2020 Silverado and Sierra together with reduced engine power and service brake messages, in some cases after a module programming event with low battery voltage. The driver may feel a hard pedal and longer stopping distance; a warning message and the brake or ABS lamp appear.
- What you may notice
- Hard brake pedal and reduced assist
- Service brake or reduced power message
- ABS or brake warning lamp on
- Likely causes
- LikelyBooster worn or not holding vacuum/pressure
- PossibleLow battery voltage during module programming
- RareFaulty boost or pressure sensor input
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €250 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.