Here is the Audiworld article that I used to retrofit a set of 2021 RS5 sportback seats:
https://www.audiworld.com/forums/a4-...rofit-3055173/, it's the first article
"Hello all,
As per the title of this thread I've recently retrofitted the super sport seats from the S4 into my A4. My A4 only had manual heated seats with lumbar support so there was a bit of extras work to be done in order to get the full elective movement to work.
Luckily my seats also came with the memory module fitted to it to this actually made my seat memory work. If you want seat memory working you will also need the door card with the buttons for the memory, as well as wiring the seat if it doesn't already come with the module for it.
So this is actually nothing complex to get this all working and was more of me just doing the research to find out what exactly was needed:
To start with I purchased this wiring kit from kufatec
https://www.kufatec.com/en/comfort-r...audi-mlb-48893
This is the correct kit to give you extra power to the seats. You only need one of these to power both seats. On the wiring harness there will be 2 pins leading to the same 2 pins, this part is for both of your front seats. They will need to be wired into the male connector that's in the floor. To remove this you can simply take out the black surround that the seat wiring connects to and then you can remove the red male plug from the other side. Make sure to disconnect the red female plug from the seat first. The 2 pins connect into slot 17 & 5. The wires will be numbered as to which one goes where. Then route the cable through to the other seat and repeat on this side. I routed my cable under the carpets through the centre console. On the sides of the centre console under the plastic trims i made a small hole in the carpets to feed the wires through. This made it easier as the carpet continues under the centre console and you cant see the hole as it sits under the plastic trims.
Once you have wired the other seat then head towards the fuse box / BCM area (this is for RHD vehicles not sure about LHD). You want to head for the T73a module which is the middle connector of the 3 black plugs. This cable is to be inserted into pin 25. Then lastly you will need to head into the fusebox and power it. Personally i just used a fuse tap as I was being lazy however power it as you wish. Once this is all done plug the red connectors on the seats back in and test out the power. You should be able to move the seats like normal and massage should begin once button is pressed! However you will notice there is no MMI control and massage / lumbar cannot be adjusted as it should be. This is where our last wiring comes in.
If you inspect the red drivers seat female plug and look at pins 13 & 14 (numbers may be wrong I can't remember exactly) there are 2 can bus wires. One orange green and one orange purple/brown. These 2 cables need to tap into the canbus to finish up the seats. Again remove the red male plug from the car and insert male can wiring into the corresponding pins for can wires. I wired them to the gateway underneath the rear seats. I found wiring it directly under the carpets too difficult so I took it back into the centre console and then through the centre console to the rear of the vehicle. Then over the hump in the middle back seat and into the gateway module under the rear bench. The orange green wire needs to connect into pin 15 and the orange brown into pin 33. Now connect everything back up but don't reassemble just yet in case something is wrong.
Some coding needs to be applied I can't remember it all I will put it here as I go along:
09 Long Coding: 07501B43E17B00CD050557191BAC84F913CB31040000000000 00000060001A810AC501B302BE05
36 Long Coding: 007813000000B0010000010101010000000000000000000000 000000000000
Address 5F 8W5 035 036 C channel ENG122227-ENG117556-Car_Function_Adaptations_Gen2-menu_display_seat_configuration adapted from not activated to activated
Address 5F 8W5 035 036 C channel ENG122227-ENG117558-Car_Function_Adaptations_Gen2-menu_display_seat_configuration_over_threshold_hig h adapted from not activated to activated
Address 5F 8W5 035 036 C channel ENG122229-ENG117723-Car_Function_List_BAP_Gen2-driver_seat_0x10_msg_bus adapted from CAN_MIB to Terminal 15
Address 5F 8W5 035 036 C channel ENG122229-ENG125834-Car_Function_List_BAP_Gen2-Seat_Pneumatic_msg_bus_0x3B adapted from CAN_MIB to Terminal 15
Then after this is done it should all be working!
Seat memory and massage / lumbar fully functioning as per S4 factory
If you have any questions let me know i will do my best to answer them
Thanks"
The Kufatec kit is to get extra power for the massage function and to get the linbus connection to the Central Electronics module. The linbus wires connect to pin 17 in both red seat female plugs and pin 25 in the T73a connector which is the middle connector on the central electronics module. The power feed connects to the pin 5 in both red seat female plugs and a hot when key on 12 volt source from the fusebox under the dead pedal. To my knowledge, most US spec A4s has seat memory, so you wouldn't have to worry about running the canbus wires from pins 13 and 14 from the driver seat red female plug to the gateway module under the rear seat. Make sure the save the original coding of the 09 (Central Electronics) and 36 (Driver Seat Memory Module) before changing the coding. I used VCDS for coding and all I changed was activating the second bit and deactivating the third bit under byte 19 in the 09 module. However, I did have to replace both lumbar support/massage modules because the 2021 modules did not work in my 2017.
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