2006 a4 b7 cab with 09L / JAX gearbox fault (P0905) - please help!!

[Sturat]

After getting my car through its MOT yesterday, I thought I'd take it for a drive.
The car has hardly any power and considering it's supposed to have 230bhp I would have expected it to manage more than 40mph up an incline!
Scanned it with OBDeleven and came up with fault code P0905 and P242F (DPF restriction)
After I clear the fault codes and its in park then the computer displays clearly that its in P position.
When I push the button on the side of the gear stick and move it down it shows the gear position on the display until I get to drive (D). When it's reached that position the indicators on the computer screen all turn solid red, they don't flash they just turn solid red.
I can move the stick to sport and the car revs higher before changing gear so I presume I actually selected sports.
If I select tiptronic the display doesn't change and stays solid red, it doesn't display the gear number, I've not tried to drive it in tiptronic yet, maybe I should try that too?
I have taken the gear shift to pieces and can't see anything burnt out on the circuit board. The magnets are still in position and I can't see any damaged wires.
The next thing I think I'm going to do is check the wiring from the gearbox control (J217) unit to the tiptronic switch (F189), then the rest of the cables from the gearbox control unit to there point of termination.
This is going to take a while so if anyone has had the same problem or can give me some advice on my next move then please let me know.

Also the lack of power issue, is that due to the dpf, gearbox fault or is it more likely to be something else?

Please give me some help if you can.
I will put all my findings on this thread.
Thanks!

 

[Sturat]

I forgot to mention on this tread that I bought the car as a non-runner and therefore I'm at a disadvantage as I don't know it's history or when these faults specifically occurred - all faults were wiped before I bought it.

I've been researching the fault code P0905 and my understanding is that there are two sensors which sense the position of the gear selection.
One is at the gear lever, sensing it's movement and the other one is within the gearbox itself also sensing it's position.
I changed the magnet round (changed it's polarity) in the rubber under the gear shift within the F189 to see if it made a difference. I think it did because now when I remove the P0905 fault and keep the gear stick button depressed I can move the gear stick and the display shows its exact position, even when it's in tiptronic.
But as soon as l release the gear stick button when in D, S or tiptronic the display shows PRNDS in solid red again and registers the P0905 fault immediately.
Please help by telling me if I'm on the right path, thinking that the F189 sensor must be working correctly and communicating with the ECU?
Also is correct me thinking that its only when the button is disengaged that the other sender informs the ECU of the gear position so that it can see if its in a matching position?
I reckon from the above that either the wiring from the automatic gearbox control unit (J217) is faulty, the unit itself is faulty or the selector lever cable needs slight adjustment?
Please give me your thoughts especially if you've had the same problem as this car is taking ages to sort out.
Cheers

 

[Sturat]

More research suggests that the gearbox is in emergency running mode due to the fault - hence no power.
I thought it may be the dpf being blocked but now I don't think it is.

 

[Sturat]

I just changed the F189 and the solid lights have disappeared and the tiptronic is working showing the gear selection.
Hope this helps someone else!