Audi A4 2017 passengers heated wing mirror.

[PHB]

The heater is working intermittently, I have replaced the glass with not change. The power to the mirror changes from 14 volts to 4.6 volts. The diver's side is working perfectly. Any ideas?

[PHB]

Could the change in voltage be caused by a bad connection on the wiring loom. I am assuming the door control module is OK as the drivers door mirror heats up fully.

[Steve Q]

Yea it could be, the wires in the door look can break over time unfortunately 

[PHB]

So I assume, although it is the passengers side wing mirror, it could be the wiring in the drivers side and possible more likely as the drivers door is used far more than the passengers side.