Honda Grace Trans Issues: Erratic Shifting + Warning Light

Hey there! I have some experience working on cars and had a very similar issue with my 2016 Honda City (pretty close to your Grace). My problem turned out to be more serious than a parking switch, it was actually a faulty transmission control unit. Like you, I noticed weird shifting patterns and warning lights. My regular workshop diagnosed it after running some tests. They had to replace the entire TCU, which wasn't cheap, cost me around 1000 Euro But since then, the transmission's been working like a charm. These issues can be tricky with modern cars. Could you share more details about what's happening? Like, does it happen when the engine's cold or warm? Any specific gears giving you trouble? Also, what's your current mileage? This might help pinpoint if it's the same issue I had. BTW, if anyone else owns a Honda Civic or Grace with similar symptoms, feel free to chime in!

Thanks for sharing your experience! My Grace has 152646 KM on the clock, and the issue mostly occurs when the engine is warm, especially during highway driving. The shifting gets really unpredictable between 3rd and 4th gear. Just had my service last month and everything else seemed fine, but this started happening about two weeks ago. Really hoping it's not the TCU like in your case, that sounds pretty expensive! I've noticed it's smoother in the morning when I first start driving, but gets worse as the day goes on. No weird sounds though, just the erratic shifting and that annoying warning light. Has anyone tried fixing this without a complete TCU replacement?

Hey again! Yeah, those symptoms you're describing sound way too familiar, especially the part about it getting worse when warm and during highway driving. When I had my City, it started exactly the same way, smooth in the morning but acting up later in the day. You know what's interesting? Before I ended up replacing my TCU, my mechanic actually tried cleaning the transmission fluid sensors and updating the TCU software. It helped for about a week, but then the problem came back even worse. The total mileage on my City was pretty close to yours too, around 150k km when this started happening. Quick tip though, before you go ahead with any major repairs, get them to check the transmission fluid quality and level. In my case, they initially thought changing the fluid might help (it didn't ), but it's still worth checking since it's way cheaper than a TCU replacement. Also, while we're talking about this, keep an eye on your engine temperature gauge. When my TCU was failing, I noticed the transmission would act up more when the engine was running slightly hotter than usual, especially in stop-and-go traffic. Let me know what your mechanic says. Really hoping you can avoid the TCU replacement route I had to take!

Thanks so much for all that detailed info! I'll definitely get the transmission fluid checked first, at least that won't break the bank You're right about the temperature thing too. Now that you mention it, I've noticed the shifting gets really wonky when stuck in heavy traffic, which is probably when everything's running hotter. I've booked an appointment with my mechanic for next week. I'll ask them about cleaning those sensors and checking for any software updates before jumping into anything major. Really appreciate you sharing your experience, at least now I know what I might be dealing with! The TCU replacement cost sounds painful, but I guess it's better than being stuck with an unreliable transmission. I'll update this thread once I find out what's actually causing the problem. Thanks again for all the help!