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Discussion Starter #1
My power brake booster won't hold its vacuum (OK, negative air pressure) for more than 2 days. This means that when I try to start it after 2 days of non-use (vehicle has a start button and I must press on the brake pedal while starting) there are no power brake applications available therefore I must press extra hard on the stiff pedal to make brake light switch contact to enable the start circuit. Then it starts and immediately, the brake booster is replenished with vacuum from the pump on the engine. After that, the engine starts as it should and continues to do so unless I allow the vehicle to sit unused for more than 2 days. My RAV4 will hold vacuum for a week, probably more if I let it sit unused. After a week it still has around 5 power assisted brake applications available BEFORE starting the engine. It does not have the push-to-start button. My 2012 Dodge Ram would sit unused for a week at a time frequently and if I needed to roll it back or forward in the shop without starting the engine I would turn the switch on, press the brake pedal with my hand, put the transmission in neutral and roll the truck where I needed it to be. No problem pressing the brake pedal.

I've taken the vehicle back to the dealer but did not leave it with them for them to recreate the problem. However they did do a leak down test and didn't find anything wrong. I recently left it overnight with another dealer but decided to take it home the next day because they had not heard of this issue. However, they did gave me a loaner to get home with (2019 Camry) that I discovered had only 1 power assisted brake application available the next morning. This vehicle did not have the push-to-start button and therefore no requirement to press the brake pedal to start the engine. I simply pressed the brake pedal to see if power brake assist was available.

My question is has anyone noticed this situation with their push-to-start equipped 3RD generation Toyotas. Or has anyone noticed the loss of power brake assisted applications BEFORE STARTING THE ENGINE on vehicles that have sat unused for any period of time.

Thank you
 

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I have noticed that if I'm in a hurry and mess up the timing between pressing the brake pedal and pushing the start button, and then I have to start over and press the brake pedal a second time to start the engine, then yes, it's noticeably harder to press the brake pedal the second time.
 

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Discussion Starter #3
toto,

Thank you for your reply. What you have noticed is exactly the issue I have. There is nothing wrong with how you occasionally "mess up" as you say while starting your vehicle. If you waited another day or so you might have noticed the hard brake pedal on the first attempt to start your engine. That's the way it often happens to me. I am retired so I do not use my Tacoma every day.

As someone who worked in auto repair for many years I am sensitive to this issue. Owners with vehicles that do not require a brake pedal application during the start procedure might never notice the hard pedal since the vacuum boost is replenished as soon as the engine starts. However, this tells me that there is a leak. It might mean that the booster has a leaking diaphragm or that the valving inside the booster is defective. It could be something as simple as a malfunctioning one-way check valve. Perhaps the vacuum brake booster is made differently and it can't hold a vacuum reserve. I've always been told that boosters needed to hold a reserve of vacuum so in case someone's engine died they would have several brake applications to bring them to a safe stop. Engines don't die much today but I would not like to run out of fuel while driving down a long, descending mountain road without the power brake reserve being there.

In my case, I do not like having to press harder on the brake pedal to start the engine after only two days parked. This reminds me there could be a serious issue. After shutting down the engine, my power brake booster has 7 - 8 power assisted brake applications which (after restarting the engine) disappear over the next two days.

I would like to hear from others.
 
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