My 22lb dog is heavy enough to set off the passenger side seatbelt warning light/sound. Never had this problem on my W203. Is this normal for the W204 or could this be a potential problem with my car - 2010 C300...thanks.

Euro standards may have changed as to the minimum weight for detection. There is also some way to disable the passenger airbag if a child under 12 (?) occupies the seat, check the manual.

In the meantime, you could just buckle the belt and then put the dog in as long as he doesn't get your seatbelt dirty...

How attached are you to the dog? An unrestrained dog thrown into a deploying air bag is more likely than not a major injury or fatality.

The dog weights 22 lbs? Take that and multiply by a possible speed at a typical impact and imagine if it gets tossed around in the direction of your head.....that's a lot of impact force on you. For example.....22lb dog in 25 mph side impact...dog coming at you with approximately 550lbs of force. Not good for you or the dog.

For the back seat.........http://www.petautosafety.com/dog-car-seat-belts

I agree with you completely and I do have a restraint for my dog...just have to ensure that going forward, it's used every time.