Disabling passenger air bag for rear facing child seat

Hi, I’ve got a 2016 Mk 3 roadster, and I’m trying to fit a rear facing child seat. I need to disable the passenger air bag and I’ve tried the method described in the manual, I can’t seem to get the seat belt to go into ‘automatic’ mode. Can anybody help?

Thanks

Pete

2016 MKIII? MKIV surely? Can you post the page of the manual you’re referring too? If I recall correctly, the passenger airbag is disabled automatically if it doesn’t sense someone occupying the seat. The sensor can tell the difference between the weight of a child seat and someone actually sitting on the seat. The sensor detects moisture from a human body to decide if it’s a person in the seat or not.

Sorry my typo, 2015 Mklll. A scan of the page attached- it suggests that a full extension of the seatbelt will disable the passenger airbag, which presumably results in a permanently flashing warning light. I’ve attached the relevant page from the manual.
Cheers

Pete
MX5 Child seat 1|590x500

Pulling the seat belt fully out and releasing it should mechanically lock it to stop it extending again until fully retracted (if your car is fitted with that feature). This fully secures the child restraint. Is the air bag not disabled by using the key in the slot next to the steering column? Or is that system an accessory option?