Since I haven't seen a basic walkthru I'll just have this here for reference for those of you who are curious what steps are needed to get this done.
2021 Model Y Performance build date of 9/21
Part# 1537264-00-B
Price: $152 after tax from Tesla San Francisco
Tools: flat head screwdriver, 10mm socket with 6 inch extention
View attachment 837270
1. Pry off the tail gate plastic protector...note i have metal pieces but its a pull straight up from the left side, give it a good pull and it will come lose very easily
View attachment 837271
2. remove plastic round clip with flat head screw driver...its the one at the top of the pic
View attachment 837272
3. remove this plastic piece...pull straight up , comes out easily
View attachment 837273
4. remove plastic clip the one in the middle and remove the entire piece for the plastic pocket
View attachment 837274
5. pry the panel with your hands pull slowly down the length of the panel...
View attachment 837277
6. unplug the rear cigarette 12v power clip
View attachment 837278
7. The ecu is behind the black plastic bracket
View attachment 837279
8. remove the 10mm bolt and slide the ecu to the right and it should come out after you unplug three connectors....one of them was a little stuck but work slowly. the car will make some sounds when you start unplugging these clips. Plug in new ecu and re-install.
View attachment 837280
9. update the software!
View attachment 837281
10. wooo!