I know it's well known for the diff pinion bearing to go noisy, which mine was. However last week on my way to work, the nearside rear wheel appeared to lock while I was doing 40 MPH. Thankfully the vehicle didn't deviate from where I was pointing, so was able to stop and then actually move off the road it by giving it some throttle.

A friend with a car transporter took it back home for me, and I assumed the issue was the parking brake, as it appeared appeared that just the LH rear wheel locked.

So I replaced all the rear brakes, finding the PB shoes and rotors in a bad way, and quite clearly hadn't been touched in many years.

Next day I needed to bed the new PB shoes, so I drove down the road at 20 with the lever up one click for about 400 yards, after which I released the lever and speeded up to 30 ish. Suddenly there was a massive bang from the rear, and I'm sliding sideways on a narrow fast Cornish road. I stopped in the middle of the road, about 30 yards from a farm entrance, so I had no option but to force the poor vehicle along the road, with the front tyres struggling for grip, and the rear tyres sliding.

It was a 3 hour wait for recovery, to take me 1/3rd of a mile back home.
As the FL2 was being loaded onto the lorry, the driver said he saw the RH rear wheel trying to rotate forward, but the LH rear wheel was rotating backwards.

This was the same but reversed coming back off the lorry once home.

So the question is. Has anyone heard anything about rear diff seizure on these vehicles. The diff planet gears are obviously still working ok, as the wheels are turning in opposite directions, but something on the pinion or Haldex seems to have locked solid. The diff was a bit noisy, but not particularly so, although I've no reference to how noisy they can be. But to seize, something pretty catastrophic must have happened to it.

I must admit that the first impressions of FL2 reliability aren't high, as I've never had as much trouble with the earlier FL1 in 10 years of ownership, than I've had with this FL2 in the 6 months I've had it.

Any help would be appreciated. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Newer heard of a seized diff, but everything is possible. The pinion bearing of the diffs I have opened does not look good, and if not replaced, the total failure will be coming sooner or later..

This is the pinion bearing from the last one I rebuilt (#9):