The C1101 code on a 2023 Infiniti Q50 indicates a malfunction in the brake booster vacuum sensor circuit. This sensor monitors vacuum pressure in the brake booster, which is essential for power brake assist operation.
Brake Booster Vacuum System
The brake booster uses engine vacuum (or an electric vacuum pump on some configurations) to multiply the driver's brake pedal force. The vacuum sensor monitors booster pressure and alerts the control systems when vacuum is insufficient for proper brake assist. Some Q50 models with the twin-turbo engine use an electric vacuum pump since turbocharged engines produce less intake manifold vacuum.
Symptom Recognition
With C1101 present, you may notice a harder-than-normal brake pedal, especially during repeated stops. The brake warning light and possibly the ABS light will illuminate. If the system detects critically low vacuum, it may disable certain brake assist features. The auto-hold and hill-start assist functions may also be affected.
Diagnostic Approach
First verify actual brake booster vacuum using a vacuum gauge - this determines whether the sensor is reporting a real condition or malfunctioning. For turbo Q50 models, check the electric vacuum pump operation. Inspect the sensor connector and wiring, located on or near the brake booster in the engine compartment. Test sensor output against vacuum readings to verify accuracy.
Repair Options
If vacuum supply is the issue (leaking hoses, faulty check valve, weak vacuum pump), address those components. If vacuum is adequate but the sensor reports incorrectly, sensor replacement is needed. The vacuum sensor typically mounts directly on the booster and is accessible in the engine compartment.