So I'm looking into the feasibility of retrofitting lumbar while bypassing Tesla's electronics altogether. It seems feasible. My plan is to use the lumbar valve body/control unit from a non-Tesla car while reusing the Tesla pump and factory switch. The BMW F30 valve body/control unit looks to be a suitable candidate - there are probably others out there.
So to explain how things work on the Tesla - The seat control switches appear to be dumb with no active electronics. Just trigger different resistances back to the front body controller which then goes and triggers the various motors and lumbar ecu.
The lumbar ecu is connected to the body controller via lin bus. It has 3 air tubes, one for the pump, and then 2 for the air bladders (upper and lower). The other connections are power, ground, motor power, and a ground passthrough for the motor. Said lumbar ECU also has some internal valves and such that it controls. So the lumbar switch signals the main body ecu with a different resistance for whatever direction, and then the body ecu commands the lumbar ecu to go up, down, in, or out - and the lumbar ecu will engage motors and valves appropriately to perform said task.
As we all now, Tesla decided for some reason that we can't be allowed to retrofit lumbar back. So now we have to bypass the tesla electronics.
Enter the BMW F30 lumbar support:
You'll notice it actually looks quite similar to the Tesla getup. Two air bladders, a motor, and a valve body / ECU. Said valvebody/ ECU seems to have the same mounting style as the Tesla piece itself.
The big difference is that it doesn't need to talk to a master body controller to work. The lumbar switch is connected directly to the valve ECU (using a similar scheme of different resistances to trigger the direction). And then it triggers the motors and valves to replicate the functionality.
Currently my plan of attack is to buy just the valvebody/ECU (relatively cheap on eBay), hook it up to the tubes and motor of the tesla piece, and trigger it using the tesla switch. Basically it'd come down to repinning a couple things at the ECU end and then running a wire from the seat control switches to the lumbar plug.
Anticipated issues:
- It's highly likely that BMW and Tesla use different resistances for the different directions. This isn't insurmountable, just have to measure resistances and change resistors on the boards.
- I'm not sure if the +12v on the lumbar connector is still active. If it is, that makes life easier (though does probably means Tesla could **** us again in the future). Otherwise we'd have to find a switched 12v source elsewhere. Not insurmountable in theory, but would add some complexity.
But yeah, this seems feasible to me, so I'm going to order some parts. There are probably lumbar control pieces from other cars that would also work, but I'm most familiar with the BMW ecosystem and have access to those wiring diagrams, which is why I looked there.
Tesla diagrams for reference:
And the relevant BMW diagrams: