Hi there
Personally I would start with a wiring check including any connectors (check pins for water ingress, corrosion, security of connection, etc.) before starting to consider condemning any of the components such as the controller or pre-charge pump. Get the back of the car up, safety first - securely support with axle stands or drive it up ramps, then take a look.
Do you get any other fault codes come up on a scan? Sometimes faulty brake pedal switches can trigger AWD fault codes. If not then the issue is highly likely to be with the AWD system.
If the wiring/connectors to the controller and pump seems OK, get an assistant to start the engine and listen to see if the pre-charge pump 'primes'. Use either a mechanics stethoscope or hold the blade of a screwdriver to the pump body and press your ear to the end of the handle. If the pump whirrs then its probably OK which would point towards the controller possibly being at fault as you have lost AWD totally. If it doesn't make a sound then its either dead or not getting power.
Hopefully this gives you something to have a crack at on the drive before getting anymore involved.
Hope this helps.
