Here is the situation. You have a vehicle in the bay and the brake booster is not working and the customer is complaining about a hard brake pedal. Inside the brake booster is oil. Next, you follow the line from the booster to the engine.
But, the line does not connect to the intake manifold. Instead, the line connects to a pump that is driven by the exhaust camshaft.
This is a vacuum pump is designed to produce vacuum to the brake booster and other items on the engine like the turbocharger wastegate and diverter valve. Why?
A lot of modern engines do not produce a lot of vacuum when the throttle is closed. In this video, Andrew Markel describes the how the pump can fail and the symptoms of a hard brake pedal.
This video is sponsored by ADVICS.
