Does anyone know if the lack of an occupancy detector on the front passenger seat will prevent the firing of the airbag and seat belt pre-tensioner on a MY08?

Due to a faulty seat heater on my driver's seat I'm going to swap the two seat bases over. It means the passenger won't have a heated seat until I can get the driver's seat sorted. I've got the bits (from Dan at Duckworth ) but changing the leather cover requires skills/tools I don't possess in order to fix it correctly. Hoping to get it to an upholsterer ASAP but won't be for a week at least.

The passenger seat is rarely used and I use the heated seat a lot in winter hence the short term swap over of bases (assuming they are interchangeable). However I don't want the passenger seat safety to go back to the early 80s and rely solely on the inertia belt. As we'll be using both seats this weekend I'd rather not put SWMBO at risk in the event of a shunt. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

A very good question.

http://media.disco3.co.uk/gallery/albums/u...tion~5.pdf

From what I can make out, the seat belt pre-tensioners will function if the belt is coupled. Sounds like it's only the NAS spec Occupancy Classification System that will fully inhibit the passenger airbag, but it's not explicit on that.

Quote:

Firing Strategies

The seat belt pretensioners are fired when either the pretensioner impact limit or the roll-over limit is exceeded. The RCM (restraints control module) only fires the pretensioners if the related safety belt is fastened. For the front passenger pretensioner to fire, the seat must also be occupied by a large person, i.e. someone over a given weight (NAS only).

The driver and passenger air bags are only fired in a frontal impact that exceeds the stage 1 threshold. Both stages of the inflator in the driver and passenger air bags are fired. At impacts between the stage 1 and 2 thresholds, the delay between the firing of the two stages varies with the severity of the impact; the more severe the impact the shorter the delay. At stage 2 impact thresholds and above, the two stages of the inflator
are fired almost simultaneously. The passenger air bag is disabled unless the front passenger seat is occupied by a large person (NAS only), or the passenger air bag deactivation switch is on (all except NAS). The time delay between firing the two stages of the inflator in the driver air bag is increased if the driver seat is forward of the seat position sensor switching point.

If there is a fault with a safety belt buckle sensor, the RCM (restraints control module) assumes the related safety belt is fastened for the pretensioner firing strategy and unfastened for the driver and passenger air bag firing strategies. If there is a fault with the occupant detection system, or if there is a fault with the passenger air bag deactivation switch, the RCM (restraints control module) increase the time delay between firing the two stages of the inflator in the passenger air bag.

If a side impact limit is exceeded, the RCM (restraints control module) fires the side air bag and the side air curtain(s) on that side of the vehicle. If the side impact limit on the front passenger side of the vehicle is exceeded, the RCM (restraints control module) also evaluates the input from the occupant classification system, and fires the side air bag only if the front passenger seat is occupied by a large person (NAS only).

The side air curtain(s) on both sides of the vehicle are fired if the roll-over limit is exceeded.

If multiple impacts occur during a crash event, after responding to the primary impact the RCM (restraints control module) will output the appropriate fire signals in response to any further impacts if unfired units are available.

Quote:

Occupant Detection System (All Except NAS)

The occupant detection system can only determine if the front passenger seat is occupied or unoccupied. The occupant detection system consists of a pressure sensor installed between the foam padding and the cover of the front passenger seat cushion.

The pressure sensor incorporates a number of load cells connected in series and embedded in a plastic film. Weight on the pressure sensor increases the resistance of the circuit.

The instrument cluster supplies a reference voltage to the pressure sensor and measures the current draw to determine the occupancy status. From the occupancy status, and the status of the front passenger safety belt (received from the RCM (restraints control module) on the high speed CAN (controller area network) bus), the instrument cluster determines the belt minder status.

This suggests to me that without the pad plugged in, the car would assume the seat is occupied as the resistance would be "high", but it would presumably recognise the open circuit and trigger a fault (either instead, or as well?).

As I say, it's certainly not explicit...  Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

Thanks for that - interesting find.

As it happens, the seat bases don't seem to be interchangeable anyway. They look at first glance to be identical but the passenger seat holes don't quite line up with the driver's frame. I note that the frames look the same so maybe it's possible with some jiggling. I note that the metal seat pans have the same number stamped on them but the driver's has an A suffix with a B suffix for the passenger's.

More worrying is that I found damage around the driver's seat pan fixings. One has significant cracking radiating from the spot weld that hold the threaded insert. The metal has deformed in this area too. Looks like someone or something very heavy has been on the seat; perhaps someone has knelt on it with all their weight when reaching across the car.

Thinking I might bite the bullet and treat myself to a whole new seat base. Get a seat pan and leather cover to go with the foam and heater I've already got and have it put together by an upholsterer. Then hopefully a bolt out/in job. As I do 2500+miles / month I think that's not unreasonable; no dissent from SWMBO when I suggested it.  2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed