C05B0Brake Hydraulic Circuit C Leak
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- C05B0 reports lost fluid or volume in a hydraulic circuit the maker designates C; at GM its meaning has changed over time. GM's 2016–2019 hybrid brake controllers used it for the front axle circuit: wheel behaviour not matching vehicle deceleration during ABS or EBD for 1 s, or master cylinder pressure above rear axle pressure at constant pedal. A 2019 EBCM with integrated booster flags dynamic leaks when a pressure error integral passes 20 bar. In GM's 2023 and 2025 tables C05B0 means air in the plunger circuit: a volume deviation over 2 cm³ during replenishment, or over 1.5 cm³ in the other tests. All Type A with MIL. GM bulletin 22-NA-247 warns of false C05B0 on eBoost models after pad work; pump the pedal firm before clearing. On 2019 Silverado/Sierra it came with Service Brake Assist.
- What you may notice
- Service brake assist or brake system message, brake warning lamp
- Longer or softer pedal travel
- MIL on (GM)
- Likely causes
- LikelyCaliper pistons pushed back during pad work and not reseated before driving (GM 22-NA-247)
- LikelyAir in the plunger or brake circuit after service or bleeding
- PossibleReal fluid leak at a line, hose, caliper or valve
- RareBrake module software calibration causing false detection (GM PIT5638)
- Repair
- Hard · Usually a job for a workshop.Typical cost: €50 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.