S80 Gearbox Issues

Sounds rough! Slipping gears and grinding noises are never good. Does it feel like you're trying to run through mud? Could be a bunch of things, but that error code is key. What did the error code say, exactly? And has the transmission fluid been changed recently? Dirty fluid can cause all sorts of mayhem.

The error code pointed towards a defective control module. The transmission fluid was changed about 30,000 km ago, so it shouldn't be that old. So you think it could really be the control unit itself? Is there a way to check that before replacing it?

Right, a defective control unit... that sounds like a pain. Could be a wiring issue but honestly, if the code points to the module itself, and you're getting all those symptoms, chances are that the module is borked. Like the brain short-circuiting! You could try checking the wiring harness for obvious damage, but honestly, I'd say bite the bullet and take it to a workshop. They've got the tools to properly diagnose it.

I took it to the workshop, and you were spot on. They confirmed it was indeed the control unit. The repair set me back about 1000€, but at least it's fixed. Appreciate your help!