Rear passenger side wheel of my 2017 Mitsubishi Triton ute is not turning

This could be a differential problem or even something like a collapsed wheel bearing. But it’s most likely to be a seized brake or parking brake that is causing this problem. Has the vehicle been sitting around for a long time without moving? That’s a common way for brakes to seize and lock the wheel, preventing it from turning.

You might be able to knock the park brake free with a bit of persuasion, or maybe crack the bleed nipple on the brake itself to let the pressure off the brake and free it. But if the brake is rusted on, then you’ll need to disassemble it to bring it back to a condition where the vehicle is safe to drive again. Even if you get it moving again, a thorough disassembly and inspection is warranted to make sure it’s 100 per cent safe to go back on the road.