near complete brake failure on my way home from Coachella

Sorry to hear about that, it sounds scary but it also sounds like the car tried to tell you.

 

with a safety issue like that, i would push them on warranty and post at nhtsa.

 

Bummer. Yep, this is exactly the type of thing that deserves a safety complaint filed w/NHTSA.

 

Sorry to hear the troubles.
$260 for an inspection is a ridiculous rip off. Who does these mechanics think they are .... brain surgeons ?!?
Unfortunately, gas station mechanics won't be able to fix these systems.

Sounds like a failure in the brake-by-wire ECU system.
Electronics do fail unfortunately and there's no manual backup.

 

There is a backup, it is the (unpowered, non-assisted) hydraulic brakes. You have to push on the brakes very hard, it's the action of your foot that powers the hydraulic brakes. You have to pump the brake to build pressure, as deltron did. Also, the "bottom" of the pedal feels higher because it is harder to depress, so it may lead you to think you've actually depressed it all the way.

It's not intuitive, so it's a good thing deltron was able to stop.

This is the same if power brakes go out in a non-hybrid car. I guess at high speeds it feels like no brakes at all. Pretty scary.

Unless there is a leak of brake fluid, then you are sort of screwed.

Anyways, during brake failure, the procedure is to pump the brakes, shift to low (or B in a Prius), apply the emergency brake, turn off cruise control, turn on hazards. Move to shoulder and/or make sharp S shape (side to side) movements if you can.

 

Sounds like the usual shoot first by trashing the Prius w/misinformation. It didn't sound right to me (and I'm no braking system expert) but your statement seems false given the below.

http://priuschat.com/forums/gen-iii...-brake-pedal-work-brake-wire.html#post1048303
http://priuschat.com/forums/gen-iii...rake-pedal-work-brake-wire-2.html#post1056888

 

Looking at the parts, it seems like what they are saying is that the Brake Booster/Master Cylinder assembly is faulty. Looks like the part cost is 1769.54 for new from trdsparks.com. I wonder if this is a part you can get from a junk yard? Hopefully Toyota just bites the bullet on this and helps you out and replaces the unit. Seems like they would want to investigate the failure given their bad press in the recent years.

 

^^ Try this site too: Toyota Parts Cheap - Genuine OEM

 

Having spent ten years in the car business, talk to Toyota's regional service rep. They should cover it under good faith warranty.

 

Wrong again idiot.

There is a hydraulic manual mode like every other car with power brakes. People just aren't used to them and don't press the pedal to the floor. This is no different than any other car 30+ years old.

 

That is just more FUD.

The DOT sets performance standards for passenger vehicle braking systems, including during partial system failure and complete failure of any single power booster or power brake unit. See CFR 49, Sec 571.135. I haven't read the whole thing, but do see some failure / impairment conditions where the allowed pedal force to stop the vehicle within the specified distance can be up to 112 pounds.

I don't see how any braking system that has no backup for a single power unit or controller failure can possibly pass this requirement. If Prii had no backup, they would have all been recalled for this during the fiasco 14 months ago.

 

While there are some common parts (eg the brake fluid reservoir), I believe most cars have at least two independent brake systems so that if a brake line is cut or damaged and loses its fluid, there's a second that still provides braking power. On my parents' old Honda Accord, the two systems were diagonal from each other.

At least for hobbit's diagram from the Gen II Prius, it looks like the fail-safe systems go to the front wheels only (though each on their own system). Plus there's also the regular system, though that looks less robust to a leak somewhere (eg if there's a leak in the normal braking system, it might have to fail over to the non-powered hydraulic system, rather than continuing to work with power assist on half the wheels). AND there's the regenerative braking too, though I don't know what the computer does with regenerative when the friction brakes are faulty; it's quite likely that it has to disable regen if it's relying on the fail-safe mode of the brakes. Engine braking (B mode) might help too in an emergency, along with the emergency/parking brake.

 

Sigh, the "regulars" here see Prius bashing in everything, don't they ?

Look, every failure mode in brake by wire systems relies on some electrical component operating or shutting down as intended. The ECU controls every electrical actuator in this design. There's no all hydraulic backup.

 

Still more FUD from tp.

You evade an extremely important point: any ECU failure mode that prevents the driver from using brute force to push through the stroke simulator to directly and manually operate the underlying hydraulic system is an extremely serious issue. It would be at least as bad as last year's whole bundle of Toyota recalls.

If DOT or NHTSA had any credible evidence that 150 pounds of brake pedal force would not override a Prius brake ECU problem, we would be hearing a lot more about it, and Prius sales would have been halted.

Having grown up with some non-power brakes, and having been trained by three Fords to push harder when the power assist vanished, I'm not yet seeing any rational reason to be afraid of Prius brakes.

 

It's a fail-safe system. You are correct that valves have to reconfigure to work in the fully hydraulic mode, but they fail over to the backup position automatically. No ECU involvement is necessary. Likewise there is no need for external power. It's a mechanical system, just like your beloved mechanical brakes.

We can propose a theoretical failure mode where the ECU goes crazy and refuses to apply the brakes while simultaneously holding off the primary backup system. It's possible, but much less likely than a total failure of a fully hydraulic manual braking system.

This is the problem with many of these "sky is falling" discussions about advanced technology and possible failure modes. Advanced technology does provide new failure modes, but often reduces or eliminates older traditional failure modes. Being human, we have already become accustomed to the older failure modes. Since they haven't killed us in the past, we discount them as unimportant. The new ones, though, are really scary. People are not rational creatures.

The brakes on the Prius are triple redundant, quadruple if you consider the super capacitor backup on the Gen II. This is better than the vast majority of vehicles on the roads today.

Tom