Honda Genuine Parts - Cap, Filler (ATF) (25615-5T0-004)

Would never have expected a critical part like this to even go bad - but it does on Civics with the CVT. Found the old one just sitting next to the fill plug, exposed and visible (behind to the left of the battery) when I went to check the old. Did a transmission flush to ensure things were good, replaced the plug - then a few weeks later, when I thought I smelled tranny fluid, the old cap was out, sitting next to the fill plug again. Called Honda, checked online - common complaint. Wasn't convinced a new cap would make a difference, but it definitely does - the new one is fits much more tightly than the original.My advice, check it regularly, at least weekly if you can - may save you $$$ for a new transmission.

OEM replacement. Like many others, my old one kept popping off. I was skeptical whether I actually needed a new one. One reviewer mentioned that the new was thicker than his old so I ordered mine. I measured the old one (in the picture) at 0.77” diameter and the new one was 0.80”. That doesn’t seem like a huge difference but after installation, it is definitely a good tight fit. If it pops again then it’s not an issue with the plug.

My last plug must have been a little old, because it kept popping out. The rubber on these is fresher, so it grips better. I haven't had any problems with the plug popping out since I got this.

2015 Honda Civic CVT cap kept popping out after ~100 miles of driving. Replaced with new cap and it's still in place after 50 miles.

This is a perfect fit and replacement. it fixed the problem of the original plug popping out.