You need a can adapter. Around £60 - 120.
You have effectively a computer that is expecting the draw of that bulb to be say 10w, you put a LED in there at say 2w and it thinks it has an 8w overload so shuts it all down - or the ECU gets confused and either it or the vehicle burn out. Either or.
Canbus is just a digital signal, the ECU is more accurate,more fussy and easily blown - but this manages the amount of electrical components we have on modern vehicles very well - the downside is, you need to tell the ECU everything that is changing by reflashing it, or use an adapter to fool it.