Audi tt haldex problem

[huwalsh]

Got a 2001 Audi TT 1.8 quarto here at the moment.
Car is only sending power to front wheels only. Error codes in ABS and ECU no communication with J492 (01324 static)
Diagnostics can not communicate with J492.
Earth strap to diff was broken , now replaced but no change. Plug connections all good and canbus scoped at diff controller signals looks fine.
So looks like controller is dead. Has anyone had any luck repairing these ?
Customer is reluctant to spend money fixing as he is selling the car.

[Meat-Head]

Well stuff the bulb up and send it on its way. Job jobbed

[Keithuk]

VAG Error Code: 01324

Fault Location:
Four-Wheel Drive Control Unit (J492) - No Signal/No Communication

Possible Cause:
No self-diagnosis is possible.

Data BUS defective.
Control unit not fitted.

Possible Solutions:
Check Data BUS Chapter 90-9.
Skoda-Fabia-Electrical

As taken from my EOBD II Fault Codes software which you can Google.