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Steve, Technician
Category: Audi
Satisfied Customers: 1427
Experience:  Garage owner for thirty years
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I have a 2015 Audi A6 C7 s-tronic. I am getting a fault code

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JA: Hi. How can I help?
Customer: Hi
JA: Hello. How can I help?
Customer: I have a 2015 Audi A6 C7 s-tronic. I am getting a fault code p0851 - park/neutral switch (input curcuit low).
JA: Just to clarify, what's the exact code? And have you tried to reset it?
Customer: Audi codes : J217 - interlock signal - P/N, Powertrain databus, 1 wire mode
JA: Are you fixing your A6 yourself? What have you tried so far?
Customer: starter interlock signal (P/N) repair group 37
JA: Is there anything else the Mechanic should know before I connect you? Rest assured that they'll be able to help you.
Customer: I am trying to find out the problem doing lots of research online about the switch but no luck. I have it booked in at Audi next week but trying my luck. They are very expensive

Welcome to JA. My name is***** am a fully qualified vehicle technician with over thirty years in the trade. I will be happy to assist you today. Hopefully we can get this resolved quickly. You will receive an offer of a phone call by the system, this only needs to be accepted if you wish to speak to me, I can otherwise continue to answer your questions via the thread.

The code is referring to the park neutral switch circuit, this is most likely the switch itself, but worth checking the connecting plug to the switch 

I hope this answers your question but I want you to be 100% happy with the answer so do please feel free to ask any further details by replying to this thread. Thank you for using Just Answer


Customer: replied 13 days ago.
A phone call would be great but there's no option.


The option should come up in a second, do you have the registration number so I can access the details please.


Customer: replied 13 days ago.

Thank you.


Steve and 3 other Audi Specialists are ready to help you

I was good to talk

The garage mentioned CLICK HERE 

Customer: replied 13 days ago.
Thank you

Your welcome, I hope all goes well.


I have attached an image of the park / neutral switch, it is in blue. The connector plug is (1).

This would be worth checking.


Customer: replied 13 days ago.
Is this for left hand drive model?
Customer: replied 13 days ago.
i've managed to take a lot off so far


Yes the manuals give the majority for the LHD models, with only drive specific details being shown otherwise.

Look like you are doing well.


Customer: replied 13 days ago.
i have checked the wiring. seems dry & contacts not burnt out or anything. i'll carry on digging more. The switch must be in there somewhere.
Thanks for you support. This helped me identify where abouts the switch is.

I hope all goes well.


Customer: replied 11 days ago.
Hi Steve
Hope you are well. I ended up changing the switch pc board & the shiftlock electromagnet while i was there but still same issue pops up. At least i have eliminated those 2 parts. The only thing i'm guessing is it's a connection at the gearbox. I would really appreciate your help if you have a quick dig to see if there is a switch anywhere on the gearbox. If you need the gearbox number again i can give it. Your help will be appreciated greatly.
Kind regards

Good Morning Fokhrul

Give me a short moment to open up the Audi Programme and I will get back to you shortly


Thank you for waiting, the control unit is internal to the gearbox with a multiplug connection, I have attached an exploded view showing the control unit and a red arrow showing where the multiplug connection is, I have also attached a diagram of the plug showing it in situ, although this is less clear.

As the control is internal to the gearbox, the only hope is that the multiplug can be accessed and checked cleaned / this may help.


Customer: replied 11 days ago.
Thank you Steve. Yes i had checked this previously with an independent garage. It was cleaned as well. Not sure what to do now. Everything seems ok. Could it be a fuse or relay? I cannot find any fuses or relays connected to the transmission.
No, no fuse or relay in the circuit, it is either in the connection or an error in the control unit.
Customer: replied 11 days ago.
ok thanks
Your welcome