A Vag-com will see it.
Not sure about your app, but this is how it shows up when scanning the car using the "Car Scanner" Android app and a generic ELM327 BT dongle:
Raw code: 939813
ECU: 08. Heater and climate
Status: Test failed, Confirmed
Volkswagen: B139813: Left front heated seat
I had mine fail under warranty around 35K and again around 60K. The first time they said it was the element and I have not done it again since.
It is controlled by the J774 Front seat heating control module, in the driver seat pan under the seat. That has an 18 ga green wire going to the hot side of the seat base element, and an 18 ga green/red goes from the lower element to the backrest element. The elements are wired in series. An 18 ga brown goes from the backrest element to ground. There is also a 22 ga blue/white going from the J774 to a temperature sensor in the seat base. It has a 20 ga brown tied to the other brown in the seat wiring harness, and they ultimately tie into a ground on the left A pillar.
The J774 heating control modules are powered through fuse 33 on panel C, which is a 30A fuse. That is behind the cover on the driver's side door opening. The fuses there are in sequential order, so 33 is the second one in on the 3rd row from the bottom.
Replacing the elements is outlined in Section 74 of the Body Interior repair manual on erWin. It requires a bunch of upholstery work to cut and reinstall all the clips holding the seat covers on.