Power Brake Assist: Description and Operation

Brake Booster Pressure Monitoring System Description

System Outline

During an auto idle stop, the vacuum inside the intake manifold decreases.

The power brake booster vacuum assist is constantly monitored by the ECM/PCM to make sure there is the appropriate amount of vacuum available for applying the brakes.

- When the brake booster vacuum is less than the reference value, an auto idle stop is not allowed.
- Auto idle stop is monitored constantly and prohibited by the ECM/PCM when detecting a sensor failure. (Two sensors monitor for the same abnormalities.)
- The IMA system indicator comes on when either or both of the brake booster pressure sensors fail.





The brake booster vacuum must reach the established point to ensure enough braking force to allow for auto idle stop activation. If the established value is decreased to the extent that braking force cannot be ensured, the engine will transition from auto idle stop to the engine idling.