996 Passenger Airbag Child Seat Deactivation Deactivation

[sundayjumper]

No, not a typo ! I'm coming at this from the opposite direction to every other thread about it, I'm removing the passenger airbag deactivation bar. Basically, I got all over excited when my daughter was born and had it installed, but nearly four years on she's only been in the car a handful of times and because I'm now fitting buckets I wanted to remove the bar as she won't be going in it any more. She prefers Mummy's Passat

But simply unplugging the bar brings up an airbag warning on the dash It had to be coded into the car in the first place, so I guess it also needs to be un-coded.

*** DISCLAIMER ***

I've read the old threads and realise anything to do with airbags is a little contentious, so to be clear, do not do this to your car. I'm presenting my experience purely for technical interest. Don't flame me.

*** DISCLAIMER ENDS ***

Going back to my Tuna just to get this un-coded seemed like a big hassle so I started researching what the thing actually does. I found THIS thread by Renntech's "ukchris" so I must give credit where it's due for pointing me in the right direction. That thread proposes this as the schematic:



Now, I'm not strictly an engineer but I do lean that way, and to me those values seemed incredibly specific. There would be a tolerance in the manufacturing of the resistors so I felt the car would only be looking for high/low resistance in the right ballpark rather than a specific value. The nearest single-resistor solution available was 240Ω + 2kΩ. Purchased from my local Maplin for 10p each. It cost me more in petrol driving there & back !

I also needed a switch. A redundant bedroom sidelight gave me this:



So then to wire it up. The 240Ω in series and the 2kΩ switched in/out by the switch. Chop off the connector on the loom and it all fits very neatly inside the switch:



I took the following measurements while putting it together:

OEM buckle
"airbag on" = 2.24 kΩ
"airbag off" = 253 Ω

The thing wot I did:
"airbag on" = 2.21 kΩ
"airbag off" = 237 Ω

It could be tweaked to make it a closer match, but (IME) it doesn't seem to be necessary - it works as it is. I get no warning light in the "on" position, and in the "off" position it flashes for ten seconds then stops.

And I'll reiterate, because I know what some people are like, do not do this to your car. I just thought it was interesting to find out how it works.