C0091
Brake Booster Performance
1992-1998 BMW 318i E36 1.8L 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
- C0022RF Wheel Speed Sensor Range/Performance
- C0023LR Wheel Speed Sensor Range/Performance
- C0024RR Wheel Speed Sensor Range/Performance
- C0025LF Wheel Speed Sensor Circuit Intermittent
- C0026RF Wheel Speed Sensor Circuit Intermittent
- C0027LR Wheel Speed Sensor Circuit Intermittent
- C0028RR Wheel Speed Sensor Circuit Intermittent
- C0035Left Front Wheel Speed Sensor Circuit
- C0036Left Front Wheel Speed Signal Erratic
C0091 on Other Vehicles
Common Questions
What does code C0091 mean on a 1992-1998 BMW 318i E36?
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 BMW 318i E36?
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 1992-1998 BMW 318i E36?
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.