The seat heaters on my 2004 EXT randomly came on by themselves.
Ended up being a burned out seat heater element pad causing the strange behavior.
First was the driver's seat back heater pad.
A year later, it was the driver's seat bottom heater pad.
I replaced each with Dorman pads I bought off of Amazon.
Both have been working great for over 6 years now.
Using a scanner that could read SRS codes, I found the cause of the airbag error in my 2003 Z-66 to be a broken wire inside the plastic sheathing right as it went into one of the connectors under the passenger side front seat.
You could not see the break since it was inside the plastic sheathing.
I had to test the length of every suspect wire under the seat until I isolated the point of the break.
After finding the break in the wire, I was able to solder the wire onto the pin and reinsert it back into the connector.
No more airbag errors for almost a year now.
Using the same scanner I found that the main wiring connectors under both front seats on our 2012 Acadia were bad.
I located a TSB for that truck and made the correct repairs.
Over two years running on this repair.
Point being, troubleshooting airbag errors is best started using a capable scanner.
Otherwise, be prepared to have plenty of ammo for the parts cannon.
Best of luck with your repairs.