f80 m3 both rear calipers sticking

[Johnk16]

2016 f80 with 72k miles started having an issue where it felt like a caliper was sticking and come to find its both of the rears sticking to the point the car is hard to move under its own power. Hit the brakes then let off and you can’t spin either rear wheel by hand even after your foot is off the brake. Crack a bleeder valve open, fluid sprays out with some pressure then you can spin both wheels again. Both rear flexible hoses coming off the calipers seem to be clear when I blow air through them. I dont have any ABS codes, im hoping it’s not a module / pump issue but im not sure what would be holding up both the rear calipers at this point. Havent found any TSB’s relating to this nor can I find anyone with a similar issue after some google searching. Only other thing I would assume is this steel braided line (part number 34326864081) from the master cylinder to ABS pump for the rear circuit is collapsed. Any input / second opinions would be much appreciated.

[bmwdirtracer]

Electric parking brake?
Do you have any codes ?
Has anyone ever clamped off the rear brake hoses? While brake pressure of ~3000 pounds will apply brakes very well, the return of fluid relies on almost no pressure. I'd replace the rubber hoses first, because, well, they're CHEAP.

I'd likely look at replacing the master cylinder before pointing to the ABS module.

[Johnk16]

Manual hand brake, no codes or warning lights on dash and rear lines have never been clamped in my ownership. I’ve had it for 4 years, bought it with 48k miles. I’m gonna replace all the flex hoses including the ones from the master cylinder to the abs pump, if that doesn’t work, I’ll have to try a master cylinder before condemning the pump / module. I figure it’s gotta be something clogged one way or another somewhere. The fluid I do believe was last flushed in 2018/19 before I bought it. Fluid looks to be good condition still.

[Johnk16]

After further diag, I’ve found the brake line for the rear circuit that goes from the master cylinder to the ABS pump, if I crack it open on the ABS pump side the rear brakes stay locked up. If I crack open one of the lines that go from the ABS pump to the rear calipers, itll release both the rear calipers and i can spin the wheels by hand. Correct me if I’m wrong or if I’m missing something but this seems to confirm something in the ABS pump came apart and only allows the fluid to push thru one way for that rear circuit

[bmwdirtracer]

Because the ABS unit is so absurdly expensive (new), I believe I'd have a try at using ISTA to bleed the ABS before replacing it. Be aware that this job takes two people, and never seems to work unless repeated multiple times. I'd charge two hours labor at my shop, and it would likely take 2 techs more than an hour.

Of course, this might be a waste of time, because yes, it sounds like something's internally amiss in your abs unit. Have you tried spinning the wheels with the ignition on, car in neutral , wheels in air? How about with the DSC off? (Hold button down for five seconds). Or....if you have a means of clearing all the codes you'll set, you could unplug the ABS and try these tests.

That said, I would really and truly expect some kind of trouble code, if the ABS unit itself were at fault.

IF you decide to replace the ABS unit, the unit will have to be coded using ISTA, and then the system will need to be bled, as described above.

[Johnk16]

Yea I even tried with the abs module connector unplugged incase it was telling it to do this for whatever reason. I think I found a place to rebuild my unit if need be for around 400$. I will definitely try with my little Schwaben bmw scanner to try and bleed the abs pump or maybe some hard reset for the hell of it depending what options it has available before removing it to get it rebuilt. I appreciate the feedback / second opinion