Techstream Bleed vs Invalid Mode

So when flushing and refilling are you somehow emptying the system and getting air in it or how does that work usually I use a big syringe like device and suck the brake fluid out of the reservoir like down to the nothing in it and then I pour new fluid don't even worry about what kind but I put that in on top of the very little bit of the old that's sitting down there right on top of the feed ports and then I attempt to open something somewhere and let fluid out and it'll run the dirty fluid that's in the line that I'm messing with out at least which usually does something at the reservoir too so I wind up with clean fluid in the reservoir and clean fluid in the one line that I've got cracked that the fluid's running out of. And then I've got to redo the rest of the calipers. So I try not to get any air in the system from the get-go I do the same thing in my generation 2. In either I haven't gotten text stream bleeding to work. But I have good solid pedals in the ABS seems to be working well and no lights and either so I'm leaving that alone

 

You have hit the nail on the head: there are certain things you can do in Invalid Mode, which only puts the brake control to sleep so it doesn't set codes and shut things off while you are working on the lines and it thinks it detects leaks.

Brake fluid replacement is one thing you can do that way, if you're very careful, new fluid in for old fluid, no air in the system to begin with and no mistakes letting air in while you work. There is a procedure in the repair manual for fluid replacement just using invalid mode.

But sometimes people mistake that for a "non-Techstream bleed procedure", and that it is not ... as you have just learned. Bleeding the system—getting air out, if there is any up in the head-end parts—means more than just putting the brake ECU to sleep: it means getting the ECU to work all those valves inside the actuator for you, that you have no outside control over, and work them in the right sequence to chase the air out.

You may not need, literally, Techstream to do the procedure; I think it's the brake ECU that knows how, and Techstream just lets you send it the "yes, do that please" message. I believe there are some other scan tools available that also can send that.

 

Yeah likely. I’ve managed the non-Techstream brake fluid replacement a couple of times now. Was VERY careful doing the front brakes in particular, just a quick open/close blip each time, while my wife pushed brake pedal. Think you really don’t want to dawdle, have the bleed bolt open and brake pedal down to the floor. @NutzAboutBolts video was very helpful. Didn’t use vacuum either.

Pirated Techstream on a laptop (don’t currently have one) is a hurdle I’m reluctant to take on.

 

One of the best things you could do for future PriusChat readers who come across a thread like this is to stop saying things like "Invalid Mode bleed". There is no such thing. There is an Invalid Mode fluid replacement procedure. and it is in the repair manual, and it only works if there is no air to start with and no air gets in. It isn't a bleed.

You can sometimes get away with thinking it's a bleed if the only air in the system is down by the caliper ends of the lines. In a case like that, if it happens to work for you, you got away with doing something that wasn't a bleed.

To do a bleed, you need to tell the brake ECU to do it.

 

On many cars, you can use a scan tool to activate the ABS pump during a second bleed procedure. This loosens bubbles. It’s not usually needed unless the reservoir ran low. That’s probably what is being described here.

 

The guy making the video did finally relent and use a scan tool to trigger the proper bleed procedure. So that is what was described here, if you watch enough of the video. Edit: I was thinking of a different thread and different video, see correction below.

It's about more than just running the pump, but also which valves get opened so the air has a path to follow.

 

Wait a sec .. I'm sorry, I was reading too quickly and confused this thread with a different recent one where some other video suggested just driving around a field and jamming the brakes, or doing the same thing up on blocks, was a way to trigger the ABS and get the air out. In that video, he ultimately relents and uses the scan tool before his issue is fixed. (He's also working on a Trailblazer, not a Prius, but it wouldn't work any better in a Prius.) I think Rebound's comment about activating ABS to loosen bubbles made me think of that other thread.

In this case, we've just got a video where somebody uses the invalid mode fluid replacement procedure but calls it a brake bleed, and happens to get away with it. You can get away with it sometimes, depending on where in the system the air is that you need to get out. (You can also think you got away with it, while air remains in places where you don't notice an effect on normal braking.)

 

He says "bleed" but in fact it's a replacement. He's more-or-less following the non-Techstream brake fluid replacement procedure from Repair Manual.

 

If there's air anywhere near the calipers, I think brake fluid change would help. I think you can also introduce air, if you're late closing the bleed bolt. I think @NutzAboutBolts video illustrates well the front brake technique, with split screen showing the assistant's foot pushing the brake pedal. You want to do lots of little blips, close it fast.