Mercedes GLK Diesel Electrical Gremlins

Sounds like a CAN bus issue. The Controller Area Network (CAN) bus is the car's nervous system, allowing electronic control units (ECUs) to communicate. A bad connection can cause seemingly unrelated problems because modules aren't getting the data they need. When you say 'BUS system' do you mean the CAN bus specifically, or something else? Have you checked the main grounding points for corrosion? A bad ground can mimic CAN bus problems.

Yes, I meant the CAN bus. I haven't checked the grounding points yet. Where would I typically find the main grounding points on a GLK?

Grounding points are usually attached to the chassis near the battery, engine block, and possibly near the ECU itself. Look for thick black wires bolted to bare metal. Since you are seeing multiple system failures, a flaky CAN bus connection is probable. Given the age and mileage, it's worth having a workshop run engine diagnostics to pinpoint the issue to a specific connector or module on the bus. It could save you a lot of time and headache. Just a heads up, depending on the location of the defective connector, the repair cost could be around 155€.

Thanks for the advice! I took it to a shop, and they confirmed it was a defective cable connection on the CAN bus. They replaced the connection, and everything seems to be working fine now. The final bill was indeed around 155€, so your estimate was spot on. I appreciate the help!