Prius Brake Question

welcome to priuschat! no idea, but i'm sure some helpful member will be along soon, all the best!

 

Whats the brake fluid level look like?

 

Welcome to PC.
The reason your battery depletes quickly in drive is because unless you have your foot firmly on the brake pedal "this cancels the drive" the car is trying to move forwards as with any automatic, "the parking brake does not cancel the drive" even without the engine running. This will soon discharge the HV battery.
As Edthefox5 said first check the brake fluid level, but it may be the brake ECU requires calibrating "Linear solenoid calibration". This can only be done by a Toyota dealer unless you have a Mini VCI and Toyota Techstream software, in which case you can do this yourself.
Failing this I am afraid this may get expensive requiring parts, maybe a brake actuator.

John (Britprius)

 

I'm thinking its this. Bring up the arrows screen on the MFD. If there are orange arrows from the battery to the wheels when you're stopped, push down a bit more on the brake pedal.
The brake pump shouldn't run all the time unless you're pumping the brakes. Even if it was running all the time, it shouldn't draw enough power to cause the HV battery to noticeably drain.

 

I would also ask you to consider that it may not have as much to do with the brake (except not pushing hard enough) and more to do with your A/C running when you are stopped or in very slow traffic. Your HV battery will get pretty low before the gas engine kicks on. This is because the A/C has an electric/inverter compressor and doesn't run off the gas engine, but off the hybrid battery. Your HV battery charge will go pretty low (Prius trying to get you the best mileage) running the A/C before the gas engine starts to run the Motor Generator 2 to recharge the HV battery into it's comfort range State of Charge.

 

I'm wondering if the power-assisted braking system might have a vacuum leak somewhere. Not quite sure how this system operates, but the electric pump must be evacuating an accumulator somewhere. A leak might result in more frequent operation of this pump. Maybe?

 

The brake system does not work on a vacuum pump. It works buy pressurizing brake fluid into a bottle with a nitrogen filled bag. If there is a leak it is likely to be an internal loss of fluid in the brake actuator.

John (Britprius)

 

Bad guess. Once again I am amazed at the technology.

 

You mentioned that it drains the battery when in the drive-through, but not when in "PARK". Are you putting it in "NEUTRAL"? If you are, the Prius engine won't recharge the hybrid traction battery when in NEUTRAL. Some Prius owners avoid car washes that move the car through on a track with car in neutral because of this. Make sure you don't have the car in neutral. The gas engine should recharge the HV traction battery, but only to a minimum level when stopped and in drive, trying to get you the best mileage. I think you may be assuming the noise is a brake problem when it's really not. It's probably just the Prius changing between charging and discharging cycles to maintain the preferred State of Charge. Check out the video on Weber State University about the Prius Hybrid Engine and the design of the Transaxle. They have videos of other hybrids too. Watch the Prius. 15 minutes invested will help you avoid misinterpreting things the Prius does as problems and love it even more.