[aquik92]

I posted another thread before but didnt include details and left it very vague but now im armed with more info, so here goes.

So I dont have reverse lights, no PDC (neither acoustic or visual via idrive) and no auto tilting of the passenger side mirror BUT I have no error codes, R is displayed in instrument cluster, displayed via LED on the shifter and transmission works flawlessly. The strange thing is that once in a blue moon, all those issues WORK for around a second and all disappear immediately, without continuity, without warning. All this without any codes of any kind. When I bought the car, i had codes for reverse light bulb failure but did an LCI taillight retrofit and coded those checks out.

I attempted INPA for any activations which might show me if the car is recognising R, checked the wiring on the gear lever, checked wiring in the trunk, no breaks and checked fuses but all are good.

In the link posted, the car was constantly in reverse, and if you notice, the idrive screen flickers, as if its got a bad ground or not enough power? Battery not even a month old.

I believe I can solve this, basically what i would like to know is how the R signal operates in an auto transmission because if its working, even if sporadically, all things are in place and its a question of something which isnt quite connected.

Any help appreciated. Thanks!

[therealdb1]

I believe that for an auto gearbox the reverse signal is generated by the gearbox control module rather than a physical switch like in a manual transmission.

In your case it is not happening and a fault code is not generated because it doesn't know the reverse signal is not being received.

The reversing lights themselves are driven by the footwell module I think so there could be a faulty connection to the gearbox module, the footwell module or one of the modules themselves at fault.

It's a case of checking signals along the line from the gearbox module until it disappears. Quite a diagnostic task ahead I'm afraid.