Brake Vacuum Switch
WARNING: This page is about a different car, the 2019 Jaguar XJ and 2018 Jaguar XJ. However, it is still accessible from the selected car via links, so may be relevant.
To ensure the brake system is never compromised, a brake vacuum switch is installed on stop/start vehicles to monitor vacuum reserves in the brake booster. The brake vacuum switch is mounted in the vacuum pipe and hardwired to the ECM.
If the brake vacuum decreases below a set threshold while stop/start is enabled, the ECM either:
- Restarts the engine to replenish the vacuum reserves.
- Inhibits the engine shutting down if vacuum reserves are not sufficient.
An example of vacuum reserves depleting, is by the driver repeatedly pressing the brake pedal while the engine is shutdown during an auto stop/start stop. This action will initiate an engine restart when vacuum reserves decrease below the set threshold.
If a fault develops with the brake vacuum sensor a Diagnostic Trouble Code (DTC) will be stored in the ECM.