I'm currently going through this drama - didn't pay close attention when I was putting my brake system back together. Went to bleed my brakes, started at the RT/Rear as service manual states. No dice, no fluid, no nothing. Went to LT/RR - same. Just to check, did the LT/Front - got flow. Same with the RT/Front... Weird.
Decide to "gravity bleed" - nothing out of the rears after 4hr.
Start researching and find out that these valves will apparently block off one side of the brake system if it detects a leak on that side (guess it did so when i went to start bleeding the rear first - or it never was centered, one or the other) - supposed fix once installed and tripped is to open bleeders on the side you have flow from and jam on the brake pedal to "sense a leak" and effectively force the valve to trip that side and shut those off, get fluid flow to the other side and eventually you can make the valve "recenter" when you're properly bled. Tried this multiple times, different ways, no dice.
Started physically inspecting the valve. My old valve has a pin sticking out of the end of it that you can push and pull on, and you can actually see the valve moving through the end back and forth. The new style valve i have, you cannot grab this pin if it is shifted to the rear, it is flush up against the housing of the valve (UGH!) I can BARELY grab the end of it with a pick from behind and pull it forward but can't get it far enough out to get any kind of grip on it and hold it to try to get some flow to the rear.
My recommendation to not end up in my state of "screwed" and having to redo my brake lines and stuff, is to make sure the new valve is centered before you install it. They do show to have a tool that goes in where the "brake warning light" sensor goes on the top of the valve that will hold the valve in the center while you bleed. Once you're all bled, you remove the pin and reinstall the sensor and you're good to go. Pretty sure i'm gonna have to remove my valve, recenter it and go this route as anything I've tried to recenter it installed has yielded no results.