Upgrade to Heated Seats 2020 Sierra Elevation - Not Working - BCM flash

roccod787 · March 6, 2023

I replaced my stock cloth/manual seats with OEM powered leather heated seats in my 2020 Sierra Elevation from another GM (same year) truck. Plugged right into the old harness, and the power function is working (moving the seat forward/backward etc). I also installed the new climate control user interface on the center dash so that I now have the OEM seat heater buttons. Problem is nothing happens when I press the seat heater button. I've checked the fuses and all good there. I read online that the dealership needs to reprogram the BCM (Body Control Module). Also noting I do not have the digital heated seat controls on my stereo screen like the trucks with stock heated seats do. One GMC dealer is telling me that for $200 they will try to reprogram the BCM, but cannot guarantee it will work. Has anybody done this before? It is as simple as telling the car "enable heated seats option" so that the BCM will recognize the new buttons in the dash? Another GMC dealer I talked to won't even try to reflash the BCM because they don't believe it will work, telling me the BCM's are VIN specific. If that is true, I am wondering if I will need to give the dealer a VIN from a similar model that does have stock heated seats, essentially tricking the computer to allow it to upload the correct options.

PS: Same issue with the trailer brake controller. The center dash I pulled from the other sierra had the controller as well, so i swapped out my blank plug with the controller (all the wiring was there behind the dash) but nothing.

Z714Mike · March 6, 2023

Our trucks now a days seem to be computers on wheels .
as long as the additional wiring under the hood is there, reprogramming the bcm will work.
same process as adding fog lights., If I didn't update the factory wiring harness, would not have worked.
good luck.

newdude · March 6, 2023

1 hour ago, roccod787 said:

I replaced my stock cloth/manual seats with OEM powered leather heated seats in my 2020 Sierra Elevation from another GM (same year) truck. Plugged right into the old harness, and the power function is working (moving the seat forward/backward etc). I also installed the new climate control user interface on the center dash so that I now have the OEM seat heater buttons. Problem is nothing happens when I press the seat heater button. I've checked the fuses and all good there. I read online that the dealership needs to reprogram the BCM (Body Control Module). Also noting I do not have the digital heated seat controls on my stereo screen like the trucks with stock heated seats do. One GMC dealer is telling me that for $200 they will try to reprogram the BCM, but cannot guarantee it will work. Has anybody done this before? It is as simple as telling the car "enable heated seats option" so that the BCM will recognize the new buttons in the dash? Another GMC dealer I talked to won't even try to reflash the BCM because they don't believe it will work, telling me the BCM's are VIN specific. If that is true, I am wondering if I will need to give the dealer a VIN from a similar model that does have stock heated seats, essentially tricking the computer to allow it to upload the correct options.

PS: Same issue with the trailer brake controller. The center dash I pulled from the other sierra had the controller as well, so i swapped out my blank plug with the controller (all the wiring was there behind the dash) but nothing.

The brake controller can't be done so don't waste any more time on that. Aftermarket controllers are your only option there.

As for the heated seats, GM won't help as they don't offer a factory upgrade path to heated seats. You will have to try contacting White Audio and Media (WAMS) for custom spec BCM programming. The dealer trying to use another VIN will do nothing but create a rats nest of VIN mismatch issues amongst all other modules in the vehicle.

Edited March 6, 2023 by newdude

a1smith · March 6, 2023

1 hour ago, roccod787 said:

recognize the new buttons in the dash? Another GMC dealer I talked to won't even try to reflash the BCM because they don't believe it will work, telling me the BCM's are VIN specific.

The BCM is basically the same for all trucks in the same model year; they are not VIN specific. The code in the BCM is also not VIN specific. What is VIN specific is the calibrations in the BCM - they are set for the specific options in your vehicle. So you will need to get the BCM reflashed where they enable the RPO code for the seat heaters. Also, IIRC, there is also a local seat heater controller that is under the seat - I'm pretty sure the BCM is talking to the seat heater controller over the LIN bus. The seat heater controller is not VIN specific, it is specific to that seat.

roccod787 · March 7, 2023

3/7/2023: Took the truck into GMC today to find out my truck does not have the complete/correct wiring from the dash to the seat, which is why the user control buttons don't illuminate when pressed. I've contacted harnessdr.com to see if they can provide the retrofit wiring. Will post here once I find the solution.

3/11/2023: I took apart both driver/passenger side harnesses today, and turns out I DO have the correct wiring. Every single male pin on the seat side harness matches up to a female connector/wire on the truck side harness that runs to the BCM. Seems the dealer either 1. Was not wanting to mess with BCM factory settings, or 2. I need of glasses. Didn't stop them from charging me $192. I also confirmed my truck has both fuses, F6 and F17, which were factory installed, that are specific to front heated seats, option code KA1.

I've contacted another shop (non-dealer) who has the tool to flash the BCM.

Edited March 11, 2023 by roccod787