Suppressing Safety Restraint System Fault errors due to removal of rear seat?

[dbherrick]

I hope someone can suggest a solution. I enjoy camping and to obtain a fully flat sleeping area I removed the rear seat (good video on YouTube on how to do this) and built a small platform there. However, when you remove the seat, 3 errors are constantly displayed: Rear safety restraint system fault (RCM2_a857, etc.).
The errors are distracting and I want to get rid of them while the seat is removed. I supposed it could be done in software, but I'm sure that is not easy.
My second idea was to purchase spare rear seat wiring harnesses and plug them in, but that is pretty expensive and I'm not sure it would work.
Third idea, and maybe the best, would be to purchase two connectors (matching the type currently used to connect the seat harnesses) and making 'jumpers' that would fool the system into thinking that the rear seat is in place.
Does anyone have any idea on how this could be done? Would the spare wiring harness idea work? Any idea if the connectors are available and how they would be wired?

Thanks,
Don

 

[Jmauld]

I think the best option is to purchase rear seats and use the old harness/sensors. Otherwise you might be able to make a fake harness if you can figure out the details of the sensor in the seats.

 

[drdumont]

I hope someone can suggest a solution. I enjoy camping and to obtain a fully flat sleeping area I removed the rear seat (good video on YouTube on how to do this) and built a small platform there. However, when you remove the seat, 3 errors are constantly displayed: Rear safety restraint system fault (RCM2_a857, etc.).
The errors are distracting and I want to get rid of them while the seat is removed. I supposed it could be done in software, but I'm sure that is not easy.
My second idea was to purchase spare rear seat wiring harnesses and plug them in, but that is pretty expensive and I'm not sure it would work.
Third idea, and maybe the best, would be to purchase two connectors (matching the type currently used to connect the seat harnesses) and making 'jumpers' that would fool the system into thinking that the rear seat is in place.
Does anyone have any idea on how this could be done? Would the spare wiring harness idea work? Any idea if the connectors are available and how they would be wired?

Thanks,
Don

Take the rear seat and an ohmmeter. Trace the switch wiring (in the seat) to the connector and figure out what is connected when the seat belt is connected and when it is not. You might need to determine the wiring of the occupancy sensors, but I bet just mimicking the seat belt latch closure signal will be enough. You can either make a jumper connector and tag it onto the wires or get the make/mod of the connector from the Tesla service manual.

Get some In'NOut gift cards, and visit the local service center. Worked for me in Dallas with Whataburger cards. If you are not checked out on using a multimeter and chasing circuits, I bet you can find an acquaintance who is and will teach you.

 

[Jmauld]

you may be able to find the spec’d resistance range in the service manual.

 

[drdumont]

you may be able to find the spec’d resistance range in the service manual.

Hmmm... it would not have occurred to me that the weight sensors or the belt latch sensors might be analog. Is this something you know, or are you surmising?
I've thought about removing the seat in order to get the floor flat myself. Why this is necessary, I'll never know, Tesla is not the only brand to have this issue.

 

[dbherrick]

Hmmm... it would not have occurred to me that the weight sensors or the belt latch sensors might be analog. Is this something you know, or are you surmising?
I've thought about removing the seat in order to get the floor flat myself. Why this is necessary, I'll never know, Tesla is not the only brand to have this issue.

Thanks for the replys. I really do like the totally flat floor with the platform that I built. I went camping with it last week and it works great. I had a Model 3 and the floor was nearly flat when the rear seats were folded down. The Model Y is much worse in this respect. The seat backs have an unacceptable high angle when folded.

Regarding the comment that if I try "mimicking the seat belt latch closure signal" it would resolve the problem, I wonder about such a solution. If the seat is in place, whether the seatbelt is latched or not doesn't matter. No error shows up on the display in either case. That's normal operation. I don't need to simulate a latched seatbelt. The error showing up is not a seatbelt unlatched warning, it's a "safety restraint system fault". I'm guessing that the main computer knows that no seatbelts are there at all. The seatbelts go away when the seat is removed, and that's when the fault appears.

I probably need to create a jumper to fool the computer into thinking that the seatbelts are there. Installing spare seat wiring harnesses would probably do that, but I'm not up to purchasing those harnesses.

A seat wiring harness wiring diagram might help me make a jumper connector, but I haven't been able to find any such diagrams. Anyone have any?

Thanks,
Don

 

[ewoodrick]

What about the new Tesla mattress?

 

[GHammer]

Thanks for the replys. I really do like the totally flat floor with the platform that I built. I went camping with it last week and it works great. I had a Model 3 and the floor was nearly flat when the rear seats were folded down. The Model Y is much worse in this respect. The seat backs have an unacceptable high angle when folded.

Regarding the comment that if I try "mimicking the seat belt latch closure signal" it would resolve the problem, I wonder about such a solution. If the seat is in place, whether the seatbelt is latched or not doesn't matter. No error shows up on the display in either case. That's normal operation. I don't need to simulate a latched seatbelt. The error showing up is not a seatbelt unlatched warning, it's a "safety restraint system fault". I'm guessing that the main computer knows that no seatbelts are there at all. The seatbelts go away when the seat is removed, and that's when the fault appears.

I probably need to create a jumper to fool the computer into thinking that the seatbelts are there. Installing spare seat wiring harnesses would probably do that, but I'm not up to purchasing those harnesses.

A seat wiring harness wiring diagram might help me make a jumper connector, but I haven't been able to find any such diagrams. Anyone have any?

Thanks,
Don

I think @David99 has done this and figured out how to suppress the errors.

 

[drdumont]

I think @David99 has done this and figured out how to suppress the errors.

PLEASE let me know how you did it. I need the fully flat floor, don't carry passengers and don't want to deal with nags.

 

[David99]

PLEASE let me know how you did it. I need the fully flat floor, don't carry passengers and don't want to deal with nags.

That's what I did. I took out the passenger seat completely. It was more work than expected.

The seat itself comes out easy. The wire harness connector is under the A-pillar, to the right of the foot well. If you remove the trim pieces it's easy to disconnect. But the car will complain about missing sensors. Here is a list of things you need to reconnect to make the car happy.

Side airbag inside the seat
seat belt tensioner located at the bottom right of the seat
seat position sensor located at the front of the right rail
occupancy sensor (requires cutting the fabric)
seat heater wire mesh (requires cutting the fabric)
seat buckle sensor

There is no way to save the seat and get all these things out. I decided to sacrifice my seat completely cutting it apart. I figured if I ever want to sell the car and restore it, I will get a used seat from eBay. The Model Y is mass produced. In a few years from now I will be able to find plenty of good used seats. You don't want to reconnect the airbag and belt tensioner. In case of an accident they will go off and can cause a lot of damage and be very dangerous. Instead, get 2.4 kOhm resistors and use them instead. That will make the car think there is an airbag.

The other problem is the seat itself sits on 'stilts'. The raiser on the right side is easy to take out. But on the left side, it sits on a raiser that is used by both front seats and the center console. You can't take that out.

You can get a lot more space if you take out the structural foam under the seat and passenger foot well. There is a lot more space to gain. The duct for the rear passengers is under the foam, but it's easy to take out.

All in all, it was a lot of work and I had to toss a lot of parts, but again, they will be easy to replace if I wanted to. I have zero error messages.

 

[drdumont]

That's what I did. I took out the passenger seat completely. It was more work than expected.

The seat itself comes out easy. The wire harness connector is under the A-pillar, to the right of the foot well. If you remove the trim pieces it's easy to disconnect. But the car will complain about missing sensors. Here is a list of things you need to reconnect to make the car happy.

Side airbag inside the seat
seat belt tensioner located at the bottom right of the seat
seat position sensor located at the front of the right rail
occupancy sensor (requires cutting the fabric)
seat heater wire mesh (requires cutting the fabric)
seat buckle sensor

There is no way to save the seat and get all these things out. I decided to sacrifice my seat completely cutting it apart. I figured if I ever want to sell the car and restore it, I will get a used seat from eBay. The Model Y is mass produced. In a few years from now I will be able to find plenty of good used seats. You don't want to reconnect the airbag and belt tensioner. In case of an accident they will go off and can cause a lot of damage and be very dangerous. Instead, get 2.4 kOhm resistors and use them instead. That will make the car think there is an airbag.

The other problem is the seat itself sits on 'stilts'. The raiser on the right side is easy to take out. But on the left side, it sits on a raiser that is used by both front seats and the center console. You can't take that out.

You can get a lot more space if you take out the structural foam under the seat and passenger foot well. There is a lot more space to gain. The duct for the rear passengers is under the foam, but it's easy to take out.

All in all, it was a lot of work and I had to toss a lot of parts, but again, they will be easy to replace if I wanted to. I have zero error messages.

Hmmm... I was thinking more of just removing the seat cushion, disconnecting the Seat Heaters and perhaps defeating the Occupancy sensors. Then I would think the backs would lie flat, perhaps a wood box around the periphery for support/esthetics.

HOLD THE WEDDIN'! You refer to your Model Y, right? I have Model 3s. Now I think of it, the Model 3 and the model Y are of course totally different design in that area. When I get back from an AMTRAK jaunt this week I will pop my Model 3 seat cushion and see. I've done it before due to an unfortunate happenstance with a panicky Cocker Spaniel puppy. You don't want to know. And neither does the guy who bought the first Good Ship Venus...

 

[David99]

Hmmm... I was thinking more of just removing the seat cushion, disconnecting the Seat Heaters and perhaps defeating the Occupancy sensors. Then I would think the backs would lie flat, perhaps a wood box around the periphery for support/esthetics.

HOLD THE WEDDIN'! You refer to your Model Y, right? I have Model 3s. Now I think of it, the Model 3 and the model Y are of course totally different design in that area. When I get back from an AMTRAK jaunt this week I will pop my Model 3 seat cushion and see. I've done it before due to an unfortunate happenstance with a panicky Cocker Spaniel puppy. You don't want to know. And neither does the guy who bought the first Good Ship Venus...

Yes I have a Y. The heated seat element is sown into the fabric. You can't get it out without destroying the seat. Same with the occupancy sensor.

 

[drdumont]

In he Blue Bunny, the seat heaters are extant but not plugged in. And of course, since I didn't pay for the trim level, the software won't turn them on. IIRC, the S3XY buttons might, but there's really no need for them in my application.
On removing the seat cushion, there's a couple of connectors to unplug - Seat Heaters, pressure sensor...

 

[dbherrick]

OP here. Thanks for the additional input.

I didn't find removing my 2023 Model Y rear seat frames very difficult. Something like removing 8 bolts and two connectors. I'm not willing to sacrifice my rear seat like David99 did to get to all the sensors. I'm still wondering if it's possible to create a 'dongle' out of one of half of these connectors that would mimic all the sensors. Might be a profitable aftermarket accessory.

To create my platform to make a super flat cargo area, I made an oblong wooden frame that bolted to the same bolt holes (using the same bolts) as the seat frames. I connected a padded and covered plywood piece as the platform with hinges to the wooden frame. The hinges let me store the apparatus easily. Once the platform is installed, I use a folding foam mattress that I found on Amazon.

I took a look at the 'air mattress' that Tesla now has in their accessories catalog. It is really a foam mattress that inflates. It seems to pack down smaller than my folding mattress as the packed mattress appears to fit in the undertrunk cavity. However the inflated mattress seems to have a consistent thickness front to back, meaning that it suffers from the same tilt problem as having no platform and simply folding down the seats. That is obvious in the photo of the white Model Y in the catalog with the mattress in place. The mattress is clearly higher near the front, right behind the seats.

At the cost of losing some vertical sleeping space, I can think of another solution: instead of dropping the front (seat removal), raise the rear of the sleeping area. It would require 3 steps:
- create a foam wedge for the top of the seat backs (assuming no seat removal or platform here, just drop the seat backs and add a properly shaped foam wedge on top of them to make a flat top).
- raise the front cargo area floor with wooden supports to match the top of the foam wedge
- raise the rear cargo area floor (undertrunk cover) with wooden supports
Then deploy your mattress on top of the flat cargo area. I don't know exactly how much vertical space you would lose for your feet, but probably not that much.

Has anyone tried that?

Don Herrick

 

[drdumont]

OP here. Thanks for the additional input.

I didn't find removing my 2023 Model Y rear seat frames very difficult. Something like removing 8 bolts and two connectors. I'm not willing to sacrifice my rear seat like David99 did to get to all the sensors. I'm still wondering if it's possible to create a 'dongle' out of one of half of these connectors that would mimic all the sensors. Might be a profitable aftermarket accessory.

To create my platform to make a super flat cargo area, I made an oblong wooden frame that bolted to the same bolt holes (using the same bolts) as the seat frames. I connected a padded and covered plywood piece as the platform with hinges to the wooden frame. The hinges let me store the apparatus easily. Once the platform is installed, I use a folding foam mattress that I found on Amazon.

I took a look at the 'air mattress' that Tesla now has in their accessories catalog. It is really a foam mattress that inflates. It seems to pack down smaller than my folding mattress as the packed mattress appears to fit in the undertrunk cavity. However the inflated mattress seems to have a consistent thickness front to back, meaning that it suffers from the same tilt problem as having no platform and simply folding down the seats. That is obvious in the photo of the white Model Y in the catalog with the mattress in place. The mattress is clearly higher near the front, right behind the seats.

At the cost of losing some vertical sleeping space, I can think of another solution: instead of dropping the front (seat removal), raise the rear of the sleeping area. It would require 3 steps:
- create a foam wedge for the top of the seat backs (assuming no seat removal or platform here, just drop the seat backs and add a properly shaped foam wedge on top of them to make a flat top).
- raise the front cargo area floor with wooden supports to match the top of the foam wedge
- raise the rear cargo area floor (undertrunk cover) with wooden supports
Then deploy your mattress on top of the flat cargo area. I don't know exactly how much vertical space you would lose for your feet, but probably not that much.

Has anyone tried that?

Don Herrick

Sounds like a solid mod. And likely can be restored to factory if you decide to sell. I'm still trying to research the pinout of the connectors, and see how a dummy load could be constructed to fool the system into thinking the sensors are happy. If they are just contact closures that should be easy. If they are analog, hopefully its just a resistance load. I doubt they would go to the trouble of making them more complicated.

 

[dbherrick]

I did a quick web search and it looks like a couple of companies are selling the wiring diagram for $300. I think the parts catalog was freely available but I guess that document does not include the wiring diagram. Here's the link for the Model Y circuit diagram for sale...

2020 Tesla Model Y Workshop Service Manual Circuit Diagram | Super Luxury Cars Service Center

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