I keep getting a seatbelt warning when I install our car seat using the LATCH system. It's not really even the weight, since just installing the base of our Chicco Keyfit, without the car seat itself, gives me a warning. I have the seat secure, no movement laterally of more than an inch, so obviously it's putting down a lot of force onto the seat, but I don't have this same issue on my X with a lot heavier car seat and a toddler in it vs a newborn.