BMW i8 Won't Start Unless in Gear, Transmission Issue Help

Hey there! I have some experience working on hybrids and actually faced something similar with my 2018 BMW i3. The symptoms you're describing sound very familiar. I had transmission issues and error codes popping up constantly. After trying a few local shops, I found a workshop specializing in hybrid vehicles. They diagnosed a defective control unit that was causing the transmission to act up. The repair set me back about 1000 Euro, but it fixed all the problems, no more error codes or transmission slipping since then. I also owned a BMW 3 Series before, so I'm quite familiar with how these systems work together in BMWs. Could you share what error codes you're getting? That would help narrow down if you're dealing with the same issue I had. Also, how many miles/kilometers are on your i8?

Thanks for sharing your experience! My i8 has 14571 KM on the odometer since the last service. The symptoms do sound quite similar to what you described. I'm getting the P0706 and P0705 transmission range sensor codes. My regular mechanic is hesitant to dig too deep into the hybrid system, so I think I'll need to find a specialist like you did. It's really helpful to know about the control unit issue, I'll make sure to have them check that specifically. Did you notice any other warning signs before the complete repair?

Hey again! Yes, those error codes are exactly what I experienced with my i8 too! Before the complete repair, I noticed a few warning signs that might help you: the transmission would occasionally hesitate between gear changes, especially when cold, and sometimes the car would make this weird clicking sound when shifting from park to drive. I should mention that after my initial repair of the control unit, I also had to get the transmission range sensor replaced, it was actually the root cause of those specific codes you're getting. The total repair ended up being more expensive than I initially shared, closer to 1500 Euro, but it was worth every penny since it completely solved the problem. One tip: when my specialist worked on it, they found that the wiring harness connected to the sensor had some wear too. Might be worth having them check that while they're in there. Since your mileage is similar to what mine was when the issue started, I wouldn't be surprised if it's the exact same problem. Just don't let a regular mechanic experiment with it, these hybrid systems are really complex, and you need someone who knows what they're doing. Let me know how it goes when you get it checked out!

Thanks so much for the detailed feedback! That clicking sound you mentioned, I've been hearing it too but didn't think it was related. It's actually a relief to know this is a known issue and not something totally bizarre with my car. I've already started looking for hybrid specialists, and I'll definitely have them inspect the wiring harness along with the sensor. It makes total sense that both might need attention given the mileage. The cost is higher than I hoped, but like you said, better to fix it properly than risk bigger issues down the line. Really appreciate you taking the time to share your experience. It's given me a much clearer picture of what I'm dealing with and helped me feel more confident about getting it repaired. I'll update once I get it sorted out!