When I open the door of my 06 Mariner Hybrid, I can hear a compressor start - some what like the sound on a Lincoln Town car - (auto leveling) - anyone know what that sound is ? and what it accomplishes - its not when I turn the key - its when I open the drivers door.

 

Its been covered here a few times. Its an electric pump pressurizing the brakes. Perfectly normal. With the engine being able to go off you have to pressurize the brake system in an alternate fashion.

 

Thanks a lot - i never knew that - but it makes sense - I appreciate your telling me-

 

I never realized that either.

My other car, has the brakes "powered" by the power steering pump (called "hydroboost"). I just assume that the FEH/MMH used their electric power steering pump do it. I guess not.

 

They may... I'm not sure. However while you can deal with a second or two of delay on the power steering if you are pulling out.... not having brakes might make you have a bad day. So it pressurizes for anything it thinks MIGHT be someone getting ready to go. Doors opening, unlocking... etc.

 

Cool, thanks. I've been wondering the same question, but just chalked it up to hybrid uniqueness.

 

I think from a law dating to the 1960's, the brakes still need to work even if their "assist" isn't working.

I am guessing from this discussion, that the Hybrids don't use hydroboost for their "assist", but instead use an old fashion vacuum for their "assist". To do this, the Hybrids actually have a vacuum pump (the "compressor" mentioned here) to create the vacuum when the ICE isn't running????? Is that right????

 

Overstated perhaps as a complete failure, but still without the assist when you are expecting it... wouldn't be a good day.

 

From what I've heard I though it was a standard system... just using an electric motor instead of the engine for power. I know it still has brake fluid (but I don't know much else about it myself)

 

Read your owner's manuals, folks!