How many times should the brake pedal be pressed to ensure proper function of the vacuum assist check valve?

Pressing the brake pedal 2 or 3 times is the correct approach to ensure proper function of the vacuum assist check valve. This procedure allows the brake pedal to be tested under conditions that would reveal any potential issues with the vacuum assist system.

When the brake pedal is pressed multiple times, it exhausts the vacuum stored in the booster. After a couple of presses, the driver will be able to feel a change in the responsiveness of the brake pedal. If the vacuum assist check valve is functioning properly, the pedal should remain firm, indicating that the vacuum is restoring appropriately. This method effectively assesses the performance of the check valve and can help identify whether it is allowing for proper vacuum retention or if there are any leaks that could compromise braking efficiency.

Ensuring an adequate number of presses - specifically 2 to 3 - strikes a balance between sufficient testing without over-exerting the system. More presses than necessary could unnecessarily drain the vacuum reservoir, leading to potential confusion about the check valve's operation.