Recently enabled ALA on a '17 A4 Premium (B9), and to complete the modification, procured a used stalk assembly (column switch plus clock spring/steering angle sensor) with the switch combination I need from a junkyard '20 A5, part number 4N0 907 129 JN. I've checked that the airbags did not deploy in the donor car and I'm hopeful there's no hard error in the steering angle sensor making it unusable.

With that premise, I have a few question before I attempt to install and calibrate the steering angle sensor. Hoping someone can shed some light.

1. I believe that in later model years, this part is VIN-coded to the vehicle and may have component protection. If so, is it possible to either reprogram the VIN or ignore any resulting fault using VCDS?
2. If I attempt to install+calibrate the part and end up needing to go back to my original working assembly will this be an issue beyond what can be solved with VCDS?
3. Lastly: the used clock spring turns about 8 turns lock to lock. However, the external arrow marks and locking notches on the clock spring line up 1/2 turn off the physical end locks. So I can center it at either 3.5 turns or 4.5 turns, not the exact mid-point of 8 turns which is 4.
Question is - with a 1/2 turn deviation - 180 deg, will the car get mad at me and set a hard fault or recurring fault? Or can this be zeroed out via calibration using VCDS?

Any hints, links or resources here would be great! I've done a fair amount of reading and research into this, and want to understand fully what's going on so that I avoid surprises after installing. Especially since it's 30 deg and snowy outside - ESP, ABS and Power Steering are all necessary to be out in this weather!

 

I'm sure this is covered in threads in the B9 A4 and B9 A5 forums were the ALA retrofit is discussed. There's also the discussion of heated wheel retrofit, where the change of the J527 unit is also relevant, and so you'd find info there too. I think Bruce said it's not CP'd, but can't recall for sure.

 

Thanks, @SMac770 for the hints. I've read the ALA retrofit thread fully and know many folks have had success retrofitting a used part so that's good. What I gathered from the Ross Tech website/forum was that there was no CP in earlier years but was introduced later, around 20-21.

Also the specific information about the number of turns from either end on the clock spring corresponding to zero steering angle value, I've not been able to find anywhere. I'm sure the Calibration procedure will help offset small deviations, say 5-10 deg, however I just want to be sure that it can also handle 1/2 turn ballpark 180 deg without hard faults. Many folks have reported finding an internal value of 819.1 deg, only to find that it's a hard fault which basically makes the module useless when the sensed value has exceeded some range. Any hints to avoid this situation when installing a used part would be welcome!

 

Could well be something they added at the facelift (MY20). Something to annoy owners, wouldn't surprise me.

The lock to lock installed in the car is 2.9, based on the one site I could find a spec for. The Audi sites didn't seem to have anything useful.

So ±522° (±1.45 turns) installed. Allowing the coil spring to be rotated to outside of ±810° (±2.25 turns) appears to trigger that permanent code, based on that ross-tech thread. More "lets screw owners over" bs. That's not a reasonable failsafe to "make sure the cable didn't get damaged by over rotation".

I imagine this is a general non-concern if following the workshop manual process for replacing the J527 and using a unit that's not been disassembled. For those who end up doing something to the coil spring and attempt a tear down and rebuild, this would be a very relevant concern.

 

Indeed!

You're exactly right. I've checked and have just under 3.0 turns lock to lock in the car, so 2.9 seems like the correct design spec.

Understood and agreed since the clock spring can take a full 8.0 turns between its mechanical stops. It appears that they assigned an arbitrary 50% safety factor in each direction on top of the design max. steering rotation of 1.45 turns. The 8 turns the clock spring can handle equals ±1440° (±4.0 turns) which is well over that 50%, so you're right in the sense that the clock spring isn't going to be physically damaged at ±810°.


Only concern here is that there is a notch with arrow marks that line up at 180° from where the end stops are. I imagine the notch is there to prevent accidental rotation outside limits after removing the factory red tabs during the process of assembly. So I can install my used part centered at either 3.5 turns or 4.5 turns, not at 4.0 turns which would be the mechanical center of the clock spring based on the end stops. However, adding a worst-case 1/2 turn 'offset' to the 1.45 turns (which the steering will permit) is 702° which is still well below 819°. So I have a little bit more confidence now to just jump in and try this swap.

I think I know what to do on the mechanical side (take care to install with the clock spring notch and arrows positioned at 3.5 or 4.5 turns from the end stops). Same on the Calibration side - VCDS can handle that and there are enough posts on the Ross Tech forums and elsewhere.

My only concern at this point is the VIN locking and CP - is there any possibility that if the swap doesn't work out, I can't go back to my old working park and have everything work as normal? How does this normally work on newer Audis?

 

If you don't update the CP, then the car is still looking for the old unit so you can just put it back. If you update the CP, then now your original unit is "foreign" to the car. It doesn't have a history of viable units, CP has only "the one and only I want right now". But you have to directly update the CP; it doesn't happen just because you put in a different unit.

 

Got it, thanks. I'll do my homework on updating CP and get back.

 

@sammk1234 -- How did you end up with this ALA control retrofit ?

I swapped out our original non-ALA steering column control module 4M0907129GB (CCS, unheated steering wheel) with part number 4N0907129MH (ALA, CCS, heated steering wheel) yesterday and believe I found the steering wheel angle sensor to be failed mechanically with a hard DTC in Address 16, though the live data from the module suggests otherwise.

I haven't found anyone who reports a successful ALA retrofit in cars spec'ed with PR-1NB (Dynamic Steering) and module J792 (Active Steering) on the usual forums. I have another used 4N0907129MH coming in a few days. We'll see... --g

 

I haven't gotten around to doing the retrofit yet (life got in the way). Will look for any experiences/hints you can share!

 

@sammk1234 -- I just finished retrofitting J527 4N0907129MB (AV2 + 1XA, 1XC, 1XW, 2PF + 6I1 + 8T2 -- LHD/NAR, MFSW, ALA, CCS) sourced from a recycler in Michigan in our 2017 A4Q.

The hardest part of the retrofit, IMO, was getting the Active Steering control module J792 readapted correctly. Pulling the steering wheel is not too difficult, but requires care & patience (1) releasing the three catches holding the airbag module and (2) disconnecting the flat connector for the steering wheel controls.

In our case, I used a local tire/alignment shop to reset the active steering angle successfully in April when the first steering column control module I sourced turned out to have a defective steering wheel angle sensor and I had to refit the original. In this refit try, when I brought the car over to the shop to have the steering angle reset, the (kid/alignment tech) skipped the step to reset the steering angle before starting an alignment procedure. By the time I noticed him working under the car, it was too late. He had reset the toe on the front wheels to match the offset steering wheel and the car was not happy. They managed to readapt J792 OK, but the Active Steering control module J792 wasn't happy due to the screwed up front toe settings (that is, adapting the activing steering position sensors was impossible).

After a phone chat with the shop manager yesterday afternoon, I brought the car back this morning and explained the problem to their "master" tech guy, who seemed to get it -- that is, recenter the front toe/wheels with the steering wheel turned to mid-way between left & right locks and reset the active steering angle with their Snap-On diagnostic tool. After 20 or so minutes, I saw him taking the car out for a test drive -- when he got back to the shop, he showed me left & right steering wheel lock turn angles that looked close, but agreed to give the front toe adjustment another go. Another 15 minutes and test drive later, he showed me lock-to-lock steering wheel angles that were 2.5 degrees off (+393.8 to -396.3 degrees) -- close enough for me. And no DTCs !

Finally, alfter applying the adaptation in R242 (Address A5) for controlling the lane assist function by "menu" (that is, the driver assist control on J527), the ALA toggles on/off perfectly.

If you decide to proceed with the retrofit, you might want to check with a local indy shop or tire/alignment center to see whether they can reset the active steering angle following clockspring replacement easily. In our case, I was able to get the resets done for no charge on the annual alignment plan I bought a year ago (which ended today!).

And for completeness, from a VCDS auto-scan:
Cheers --g