C0091
Brake Booster Performance
2016-2021 Mazda CX-3 2.0L I4 🇬🇧
High SeverityChassis
Description
The brake booster is not providing adequate assist, detected by pressure sensor or pedal effort monitoring.
Symptoms
- Hard brake pedal
- Increased stopping distance
- Brake warning light on
- Engine may stall when brakes applied firmly
Common Causes
- Leaking brake booster diaphragm
- Cracked or disconnected vacuum hose
- Check valve failure
- Brake booster control valve stuck
- Low engine vacuum on turbocharged vehicles
Diagnostic Steps
- Perform brake booster leak-down test
- Check vacuum hose and check valve
- Test engine vacuum at idle
- Apply brakes with engine off then start engine (pedal should drop)
- Check booster operating rod adjustment
Repair Notes
Replace brake booster if diaphragm is leaking. Replace vacuum hose or check valve as needed.
Related Codes
Other Chassis Codes
- C0021LF Wheel Speed Sensor Range/Performance
- C0021LF Wheel Speed Sensor Range/Performance
- C0022RF Wheel Speed Sensor Range/Performance
- C0022RF Wheel Speed Sensor Range/Performance
- C0023LR Wheel Speed Sensor Range/Performance
- C0023LR Wheel Speed Sensor Range/Performance
- C0024RR Wheel Speed Sensor Range/Performance
- C0024RR Wheel Speed Sensor Range/Performance
- C0025LF Wheel Speed Sensor Circuit Intermittent
- C0025LF Wheel Speed Sensor Circuit Intermittent
C0091 on Other Vehicles
Common Questions
What does code C0091 mean on a 2016-2021 Mazda CX-3?
C0091 stands for "Brake Booster Performance". The brake booster is not providing adequate assist, detected by pressure sensor or pedal effort monitoring.
What are the symptoms of C0091 on a Mazda CX-3?
Common symptoms of C0091 include: Hard brake pedal, Increased stopping distance, Brake warning light on, Engine may stall when brakes applied firmly.
What causes C0091 on a 2016-2021 Mazda CX-3?
Common causes of C0091 include: Leaking brake booster diaphragm, Cracked or disconnected vacuum hose, Check valve failure, Brake booster control valve stuck, Low engine vacuum on turbocharged vehicles.