GR Yaris Recaro CS sportster with airbags

[GJR]

Pictures to follow but so far I know how to get the airbags working and have sourced the parts. Airbags test at 2.3-2.5 ohms

Now I need to look into the passenger seat occupancy sensor and how to sort that. My understanding is that in the Yaris it is just a pressure sensor but without it the front passenger airbags would not deploy. Does anyone have a solution that’s been tried before? I am thinking I either need to remove the sensor from the OEM seats if possible or use a sensor off another car. I need to test it but I believe it’s just a normally open switch that closes with the weight of a passenger.

Also anyone who looks to buy some of these seats if buying seats from another car be aware the seat bases need to be the standard ones. Some bases have different mounting holes too.

 

[TheManWithTheStick]

I'm just having some of these fitted and didn't even think of the occupancy sensor! Oh dear.

Keen to see what you come up with.

 

[Humptydumptyhadabigone]

There are a couple of different ways that weight sensors work. I haven't pulled my seats so not sure if it is a sensor on the seat frames or in the seat base. Have a look at the manual and see. Then you can see if there is an easy option.

Looks like the sensor is in the seat base... seat heater module has two connectors, the seat without heater has a connector but nothing is mentioned at all about weight sensor though the others have individual entries.

 

[GJR]

It looks like the Yaris is a fairly simple affair. The seat occupancy sensor is looking like it is just a printed carbon circuit with a polythene layer between the two circuits. Normally open loop the car does not see anyone sitting in the seat. Exert pressure and the circuit is closed and the car detects the occupant. Seat belt light on dash illuminates until the belt buckle is inserted. If you loop the sensor out the car acts as though a passenger is in the seat. It is not a bladder and gel set up which detects the weight via a control module and there are no position sensors. I now need to check with a multimeter to see if it simply is an open closed switch. If that’s the case it will be straight forward enough to build into the new seat.

There are only 4 wires, 2 go to the occupancy sensor and 2 to the seat belt buckle. The manual confirms that if there is no passenger in the seat the airbags will not deploy on that side. You could simply loop it out but would need to have the seatbelt buckle inserted to avoid the light on the dash. The audible part can be turned off with carista. Simply leaving it disconnected is not an option.

So, it is an open, closed switch but the resistance decreases with increasing pressure. I think the only option is going to be to use the sensor from the original seat. I think it’s embedded in the foam but it could be stuck to the surface like other manufactures.

 

[GJR]

Most likely a strain gauge so weight is a factor. Enquired with Toyota parts about availability. I was going to use a generic one but actually I think it will need to be Toyota specific. Anyone been brave enough to take a standard seat apart yet?

 

[GJR]

Seat bases are different on the Clio. Jon from VBD dug me out of a hole with his custom seat bases that allow these seats to mount with any seat to car mounting kit.

Should have the airbag connectors next week.

Another thing to note is that the recline adjusters are on the inside. Generic recaro seats have adjusters both sides. If you put the seats in as they are the adjusters will hit the handbrake / cup holder housing. You need to remove the adjuster bar that runs through the seat back and bring it in from the other side. Make a new hole for the shaft of the adjuster and it will all reassemble and operate the same as before. A couple of blanking caps from recaro will complete the job prior to being trimmed

 

[Tralien]

If passenger airbag wouldnt deploy if sensor didnt detect specific weight, why would you need to deactivate passenger airbag via key if you have a baby seat on it?
I think / hope airbags deploy independent from weight sensor. weight sensor is just for the seatbelt warning, not for the airbag i think / hope

 

[GJR]

The weight of a child seat is sufficient so you must manually deactivate the airbag. Found this text for a mk4 Yaris

 

[GJR]

Going to have to pull my passenger seat out and investigate when I have a few days off. Hoping to be able to access the sensor and use it on the recaro

 

[Tralien]

i just didnt connect them and i get no warning. i think airbags still deploy if i crash

 

[GJR]

i just didnt connect them and i get no warning. i think airbags still deploy if i crash

There is a good argument for that given the design. If an occupancy sensor was to fail it would likely fail open, or if the plug became detached, a wire broken etc. When it is disconnected there is no circuit and then no warning. If that were to happen due to a fault it would not be fail safe and a driver could unknowingly not have working airbags. I may pay my Toyota dealer a visit and see if the workshop will answer my question

 

[GJR]

Not my choice of background to photograph something on but I have just bought this to try as a mock up on the recaro’s. It should function the same as that in the GR. I can tell it’s a carbon printed film switch without having to take the seat apart and it only has two wires going to it. The GT86 is a lot more complicated. Next week I’ll fix it to the recaro base and report back

 

[GJR]

Picked up the airbag connectors from Lexus today. This is the part number and they are from a GS. Went to Toyota who confirmed that you cannot buy the terminals for the connectors. Waiting on the VW wiring repair set to arrive which should fit the connector. The passenger occupancy sensor is not available by itself because “this part is not supplied as an individual part because it is hard to assemble/disassemble due to structure” a seat pad is £370 and then it’s a question as to whether it would be possible. I may have a look at my OEM seats next week but not until the Jaguar seat occupancy sensor arrives to try that first.

 

[GJR]

So a little more progress. Occupancy sensor turned up. Unfortunately one side of it is not working but it was enough to see if it works. Firstly its proportions fit the seat really well. When positioned and someone is sat in the seat it goes from open circuit to closed circuit. Next I put it in the car and connected it up to the Yaris wiring loom. Ignition on, no passenger in seat no seatbelt warning light. Press the sensor and the seatbelt warning light comes on, insert the seatbelt into the buckle and the light goes off. Next I need to get Dawn to sit in the Yaris so I can check the resistance through the Yaris occupancy sensor so I can replicate the output. I’ll do that by putting a resistor inline so it’s the same or close to with the Jaguar sensor. That will mean the occupancy sensor will work and if it is weight sensitive it’ll provide the correct signal to the car for an adult.

 

[GJR]

The occupancy sensor in the Yaris gives a resistance of 30-32 ohms with me sitting in it at 75kg and 40 ohms with Dawn in it at 57kg so the weight does change the resistance. With the Jaguar sensor it’s 15 ohms for me and 20 for Dawn. I’ll use the Jaguar sensor and put a 20 ohm inline resistor in the loom from the occupancy sensor.

 

[GJR]

This has been reported by Petrov but I can confirm the part numbers are correct. In the uk you can get the plug from Lexus (you may need to have a registration number for a GS) and the VW wiring from allcarparts. The occupancy sensor is a jaguar landrover part LR028237 and I’ll use the super seal 1.5 connector for that. That’ll mean a modification to the seat loom but the rest will be OEM. Pictures have the part numbers on them

 

[GJR]

Update! Today I got this mocked up and did some more investigating. I’ll try to keep it to the point.

EU regulations are different to US etc.

From NCAP for automatic and manual systems
* Information to indicate that the airbag is disabled must be permanently displayed, when the ignition is on and the seat is occupied.
If at any time the airbag is switched from the OFF position to the ON position, the status indicator showing that the airbag is ON must signal this immediately after checking period for at least 60 seconds, regardless of the length of time the ignition has been switched on, or until the ignition is switched off again.

I have checked this in the Yaris and the airbag off light is only illuminated when manually switched off. This is also the same in my wife’s VW ID4. Even if she takes her weight off the seat with the seatbelt buckled there is no warning to say the airbag is disarmed.

The occupancy sensor has two wires. Yellow is the feed (10.3V) and the red wire is earth. When no weight is detected the voltage on the yellow measures 10.3v when connected to the occupancy sensor. When weight is applied the voltage drops to 0.05v as the sensor acts as a switched earth. This causes the warning light on the dash to illuminate as weight is registered on the seat. The resistance of the sensor changes with weight but the circuit is switched to earth and the voltage drops to 0.05v as soon as the sensor is closed. Because of this it is unlikely to measuring the weight of the occupant and is simply acting as a switch.

I put the passenger seat into the Yaris this afternoon and connected up the recaro airbag to the car using the above connectors. Plugged straight in and there are no warning lights. The occupancy sensor is working exactly as the standard seat does. Recaro CS with airbags and occupancy sensors working with the car. Now it’s time to make them pretty before there are photos. That’s not a skill I have though so it’ll be over to Steve at Edge automotive for the retrim

 

[Amanda]

Brilliant thread I’ve been following with a very keen interest, Ive got pole position in mine and the occupancy sensor unplugged

I was thinking of taking a seat apart but the problem I have the passenger buckle does not fit the pole , currently got a drivers one on passenger side

So would you say it’s safe to leave it as it is , wiil the passenger airbag go off regardless?

I was thinking of a a hybrid Yaris set up as the buckle on the more luxury hybrid is like our drivers as the seat is height adjustable on the luxury hybrids hence different buckle

 

[GJR]

Brilliant thread I’ve been following with a very keen interest, Ive got pole position in mine and the occupancy sensor unplugged

I was thinking of taking a seat apart but the problem I have the passenger buckle does not fit the pole , currently got a drivers one on passenger side

So would you say it’s safe to leave it as it is , wiil the passenger airbag go off regardless?

I was thinking of a a hybrid Yaris set up as the buckle on the more luxury hybrid is like our drivers as the seat is height adjustable on the luxury hybrids hence different buckle

I’ll have a look at the buckle wiring and see what I can work out. I suspect the occupancy sensor sensing weight and switching to earth then provides a feed to the buckle which is grounded by the seat belt. I would suspect that the buckle serves to switch off the warning light on the dash and possibly activate the seatbelt pre tensioners. If a seat is occupied but the seatbelt is not being worn the airbag will not go off. My wife attended a crash a month or so ago and every airbag had gone off with the exception of the passenger front airbag. This was in a landrover but regulations wise they are the same. No passenger was in the front. They are not weight sensitive in the GR. I will see if my local dealer will talk to me about it but they generally become unhelpful with any modification. I would consider putting a 20-30 ohm resistor across the terminals for the passenger occupancy sensor on your seat loom. This mimics the resistance of the sensor with an adult in the car. The dash seatbelt light would be on unless you have the passenger belt buckle in place though. That would keep you safe until I know more.

 

[GJR]

On the airbag side the Yaris is only two wires. A feed to an igniter and a return. The earth on the recaro wiring is not used. I have asked recaro dealers if they are polarity sensitive and they say “ask recaro” recaro say “ask your authorised recaro dealer” . I do not believe they are and I have found this information regarding this.

Amanda. As far as the seat belt buckle is concerned it is normally closed and when the buckle is inserted it is open circuit. I have not been able to get a voltage reading from the circuit though, even with weight applied to the occupancy sensor. The system is working but I expected to see a switched 12v feed to it. In theory if the two wires were disconnected and isolated it would be an open circuit and the car would think the seat belt is done up. Not relevant for my set up but does this help?