Help! Accidentally let all fluid drain from rear drum brake line and bleeding won’t refill it.

Unless you have techstream handy, try the "prius rock" method for bleeding the rears.

100K maint - 1

 

Assuming that it has ABS, there likely is a somewhat more complicated procedure required to get it to actually send fluid to each wheel when the car is not moving.

 

Are you trying to bleed without using the Techstream procedure?

I think if the system detects an unreasonable amount of fluid going down one brake line, it will leave that line valved off to avoid losing all braking, and that will prevent most faux bleeding methods from working.

 

On the prius, the brake actuator completely controls the brakes. When you normally step on the pedal the computers decide how much regeneration to do first, then it uses a pump to make pressure to work the brakes at each wheel. Your foot has no direct connection to the calipers or wheel cylinders. IF the actuator completely fails then there is a backup mode where the master cylinder will directly connect to each of the front brakes- you still have some braking but no boost.

The front brakes can be partially bled using a pressure bleeder or some other manual procedure, but the rears require a scantool (techstream) or another way to tell the brake actuator to apply and send fluid to the rear brakes. There may be "work around" methods for this on youtube but I have never tried any. You also need a scantool when you have to fully bleed the actuator.

 

A brake rock works for the rears, if the brake ECU hasn't already declared that line off-limits.

 

Dear All... I just went through this issue with my 2004 Prius. The short story is that I had to clear all the DTCs (trouble codes) before the system/ABS/Actuator would allow me to properly bleed the right rear drum brake.


I used Toyota Techstream software and cable (DIAGKING) to clear the DTCs and THEN ran the “Usual air bleed” utility to bleed the system. One of the many confusing things is that when the system has detected the large leak of fluid, and shuts off flow to that line, it still allows a small amount of fluid (a decent drip, drip, drip) to flow to that wheel when bleeding. The other “functional” lines flow fast, almost like a faucet. So, I was also starting to wonder if I had an internally failed brake hose to the right rear causing the slow/minimal flow on bleeding. I didn’t. I don’t understand why Techstream does not resume proper flow to a corner, when you have told it specifically that you are bleeding the system? Why should I have to manually clear the DTCs? Not logical from my perspective.

 

I think the answer I'll go with is the people who wrote the brake ECU firmware and the people who wrote Techstream were not the same people, and nobody told them "hey, meet up together and take all the time and budget you need to devise the most awesome possible UX for bleeding the brakes."

So the people who wrote the firmware wrote it to valve off leaky lines, which can be reset by clearing the codes. They also implemented the various subtasks that Techstream has to invoke in sequence to get the brakes bled. And if the topic came up, "whaddaya do to bleed the brakes if a line is valved off because of a leak?", and the question was "is there a way to do it?", the answer was "sure, the line isolation can already be reset by clearing the codes", and that was good enough.

 

Techstream and Toyota's diagnostic information were designed and written with the basic assumption that the only people who would be using them were TRAINED automotive technicians.

I don't think they had much consideration for the DIY crowd.

Posted via the PriusChat mobile app.

 

Or even independent professionals.