Login with vcds & see if it shows the modules.
There's 2 aux heaters as such, 1 is usually fitted in the car in say countries like Norway & heats up the inside of the car prior to using in the morning, this doesnt have the car engine running just uses car fuel to run & then there's one that only works at certain times as below with car running fitted to all diesels afaik & here's some blurb:
An electrical auxiliary air heater is installed in diesel vehicles. The electrical auxiliary air heater is a combination of a PTC heater element with an integrated control unit. It is installed downstream of the heat exchanger and provides additional heating of the vehicle interior after cold-starting the egine. The electrical auxiliary air heater directly heats the air which enters the vehicle interior. It acquires all information needed for operation via the convenience CAN data bus.
The electrical auxiliary air heater is activated:
- in the case of the 2C-Climatronic and Climatic: automatically via the CAN data bus; in the case of the heating system: if the occupants set the heating output to over 90% at the operating unit (analog signal),- if the water temperature is below 75Â°C,
- if the engine speed is higher than 500 rpm,
- if no load management system is active and
- if the ECON button is not pressed.