Have you had a look behind the dash on the passenger side. Sometimes vehicles have the wiring for the airbag even if there is no airbag and a dummy instead of the airbag. And you could have a bad connection or wiring fault on that.

Edit- Just another thought I'm sure on some Renault vans you need to configure the airbag ecu with which airbags are fitted to the vehicle. Something to check if you get it on a dealer tool. Maybe it's been messed with before you got it.

Chris.