Super confused about brake bleeding

I have done this exact repair with a $250 used ABS module from facebook marketplace. You will need to use Techstream utility to perform a linear valve offset/relearn procedure and a brake bleed after installing the part. The valve relearn should occur automatically during the brake bleed procedure if you select that you have replaced the ABS module. This is the only method that will remove the trouble codes and ensure your new ABS pump works properly. There is no good way to do this without Toyota software.

Used parts are a bit of a gamble, I got lucky with mine but have heard some people are unable to successfully complete the linear valve offset with a used part and they end up having to repeat the process all over again with a new part. The bleed procedure is super easy, one person can do it by themselves and Techstream walks you through each step.

 

In Techstream, you see two different menu options: a longer procedure for when work has been done on the head-end components and air might be in there (which won't all be bled out unless all the right valves get opened at the right times) and a shorter procedure for when you've just done normal stuff like changing a brake caliper and the only air might be down there. When that simpler procedure is all you need, you can often get by without the scan tool, just doing what Grandpa would have done.

Part of the confusion begins earlier, with confusion about the difference between "fluid replacement" and "brake bleeding". "Fluid replacement" is when there isn't any air in there, you're just going to let old fluid out while pouring new fluid in and you won't be letting air in. By contrast, "brake bleeding" is when there is air you need to get out of the system.

When you are reading about procedures involving ECB Invalid mode, you are reading about fluid replacement procedures (which often get called brake bleeding by people who don't know better).

You don't need to fuss with ECB Invalid mode or the like when you're really bleeding the brakes, because when you're really bleeding the brakes, you're going to go straight to the "bleeding the brakes" selection on your scan tool, and do that.

Brake warning lights are not spam. They tell you when something hasn't gone right, or what step needs to be repeated, or some other important fact about the brakes. It is natural to want no warning lights when you're finished, but that's because you want no brake problems when you're finished, not because the warning lights are spam.

There are a number of commercial scan tool options that can do the same bleed procedure Toyota Techstream can. The totally free open-source alternatives generally can't, because the commercial scan tool makers can afford to license the Toyota protocol details about how the tool kicks off the brake bleed procedure, and the free project developers typically can't.

Many around here are using the Autel AP200, which can do the full (longer) bleed procedure. An odd quirk with it is that it hasn't got the shorter, brake-lines-only bleed option Techstream offers. No big deal, doing the longer procedure when only the shorter one might have been needed doesn't really hurt anything (other than maybe your effective hourly pay, if you're keeping track).

The longer bleed procedure is supposed to wrap up with a relearn of the linear solenoid offset, but that doesn't always seem to take. If it didn't take, you'll have warning lights when you're done, and the code will be the one that tells you to re-do just the offset learning part, so you do that, and then you're done.

The offset-learning procedure also has a way you can trigger it with just a jumper wire, if you don't feel like using the scan tool to do it. (At least, I know it's that way in gen 3—I'm assuming also in gen 2.)

By the way, the reason you see a bleed procedure mentioned as a 'fix' for a goose-honk noise is that the goose honk indicates (I'm pretty sure) bubbles present inside the actuator, so that extra fluid has to rush through the valves as the bubbles get compressed and re-expand as you apply and release the brakes. The bubbles may be of nitrogen slowly leaking from the accumulator, and if that leak is slow enough, bleeding those bubbles out may banish the honk noise for quite some time, and push off the day you'll need new parts. Bleeding does not actually fix the underlying slow accumulator leak in any way, but the leak can be slow enough you won't have honks again for a year or so. Or it can be fast enough you have them again in a week.

"ABS" is only one tiny part of what a Prius brake actuator does; we normally just call it the actuator.