Defender Transmission Slipping, Parking Switch Problem?

Hey! I have some experience working on cars, and I actually dealt with something similar on my 2018 Range Rover Sport with the 2.0L gas engine. The symptoms you're describing sound exactly like what I experienced. Initially thought it was the parking switch too, but turned out to be a faulty transmission control unit (TCU). My dealer's diagnostic showed the TCU was sending incorrect signals, causing those weird shift patterns and warning lights. Had to bite the bullet and get the TCU replaced, cost me around 1,000 Euro, but it fixed the issue completely. The Discovery has a similar transmission setup to your Defender, so it might be worth checking. Could you share more details about when exactly this started happening and if you notice any specific patterns (like does it happen more when the engine's cold or hot)? This would help narrow things down.

Thanks for sharing your Range Rover experience! Interestingly, my symptoms started right after my latest service, which was about 2 weeks ago. I'm at 168206 KM now, and it's really starting to worry me. The slipping mostly happens when the engine's warm, especially during highway cruising. At first, I thought it was just a software glitch, but the warning light keeps coming back. Haven't noticed any weird sounds, but definitely feel the jerky shifts. Did your TCU replacement require any special programming afterward? Just trying to get an idea of what I might be in for if it's the same issue. Really hoping it's something simpler though, these repair bills can get pretty scary!

Hey again! Really interesting that your issues started after the service, that's quite different from what happened with mine. In my case, the problems began gradually over a few weeks, not suddenly after maintenance like yours. Given that timing, I'm actually wondering if something might have been disturbed during your service. When they did my TCU replacement, they mentioned that even slight disturbances to certain sensors or connections can trigger these symptoms. My repair did need reprogramming afterward, took about an hour extra, but it was included in the total cost. But here's what's making me think twice about your case, the fact that it's happening mainly during warm highway cruising. Mine acted up out of nowhere, regardless of temperature or driving conditions. Have you checked your transmission fluid level and condition? After my whole TCU saga, I've become pretty paranoid about maintenance and learned that low or degraded fluid can cause similar symptoms. Maybe get them to check if anything got knocked loose during the service first? Could save you from the expensive TCU replacement I had to go through. The jerky shifts are definitely concerning though, don't wait too long to get it checked out. These transmissions are pretty complex beasts!

Thanks so much for that detailed response! You've actually given me a new angle to consider, I hadn't even thought about something getting disturbed during the service. That makes a lot of sense, especially since the timing matches up perfectly. I just called my service center, and they agreed to check the fluid levels and connections first, free of charge since it started right after their work. They mentioned they'd specifically look at any sensors that might have been disturbed during the service. Fingers crossed it's something simple like that rather than a full TCU replacement! Really appreciate you sharing your experience, it's super helpful knowing what the worst-case scenario might cost. I'll definitely keep you posted on what they find. These modern transmissions sure are complicated, aren't they? At least I know what questions to ask now when I take it in tomorrow!