2012 Audi A6 C7 Parking Sensor Issue

[AvenHere]

I have a 2012 a6 and have been having some parking aid issues. The code shown is,

"B107A14 - Supply voltage for park assist sensor: Open circuit/short circuit to ground".

If any sensor was dead it typically says front left censor open, etc. but this doesn't. Ive tried countless troubleshooting options. The sensor harnesses (both front and back) read 12v when NO sensors are plugged in.
once I plug a sensor in (regardless of which socket I use) the whole system reads 2v to any sensor plugin socket. Ex. plugging in a sensor up front (only one) would make the rear socket read 2v (was 12v before plugging a sensor in) and this was the case with any combination of plugging in and testing a different sockets voltage.
Ive tried this method with COUNTLESS amount of sensors. I tried with every single existing OEM sensor I had plugged in one by one and they all shut the system down to 2v from 12v. This code cannot be reset, it instantly comes back as permanent even when all sensors are plugged in. Obviously parking aid doesn't work, + backup camera doesn't get triggered. Backup camera only works for a split second once I attempt to reset the code. What could this be?? any ideas? Please let me know if any more info is needed!

[Mesquite77]

The J791 parking sensor control unit should have a 12 pin connector(brown, middle connector), pin 1 (brown/white) is the ground, and it is shared to all sensors as you have discovered, however they use separate front and rear ground points so they may not be the problem. Pin 2 (black/yellow), is the hot, and it is also shared to all sensors, so if there is a bad wire/connection on this wire it could be a problem. Maybe try measuring resistance on this wire from the J791 to the wiring harness connection or a sensor and compare to the ground wire? Check ohmns from ground to hot of disconnected T12 plug with all sensors off?

I have fixed some gremlins in control units by pulling the fuse for a while, easy to try: 4 - Fuse 4 on fuse holder B -SB4- 5 A - Onboard supply control unit -J519-
Park assist steering control unit -J791-
Parking aid control unit -J446-


BTW, J791 is integrated in J446 Parking aid control unit in luggage compartment (rear right)

This from my 2013 A6 (built in 2012) wiring diagram, should be the same I think...

[AvenHere]

I have individually tested each harness to no avail. I disconnected the front harness from the module itself and the rear harness is still popping up the open ground/short ground code only when a sensor is plugged in. I unplugged the rear from the module and the front does the same, code pops up when sensor is plugged in and goes away after the sensor is taken out. Also, pulling fuses unfortunently didn't do anything. Any other ideas? It is a bit confusing that disconnecting the harnesses still caused the open/short grounds to be there as I thought it may have been due to a harness wire damage but I guess not it seems?

[Mesquite77]

What if one of the sensors is bad, and unless all sensors are in you will get an open circuit error, so long shot try getting one new sensor, and one by one replace and test to see if while all sensors in and if one is bad? Tough one...

Also, wondering about testing the 12V supply at a socket connector using a test light (instead of a voltmeter, to put a small load on it) with all sensors disconnected to see if there is an iffy connector or 12V wire...

[AvenHere]

Yea I have tried 10+ different sensors in all different combinations, an open ground is triggered not an open circuit, interesting.

[Botbasher]

Yea I have tried 10+ different sensors in all different combinations, an open ground is triggered not an open circuit, interesting.

But have you tried a new module? Trying new sensors and coming up with the same fault repeatedly would lead me to the module being part of the issue.

What preceded this fault? Damage from accident? Cut wiring? Anything?

Don't get so focused on the sensors that you forget that they are controlled by a module that has just as big a possibility of being the fault as the sensors!

Happy troubleshooting!

KS

[Avantly]

When checking the harness, did you check it with the sensors plugged in? If you are collapsing to 2V (and not 0V) then that indicates that you still have some continuity wherever the break in the circuit is (i.e. it's not completely open circuit) and a multimeter may still show a relatively low resistance on the harness.

If you haven't checked with the sensors plugged in, I would do that, and instead of measuring in resistance mode, measure in voltage mode. Plug the sensor in, measure from the ground side of the sensor to vehicle ground. That should be very close to 0V. Now measure from the +12V side of the sensor to the 12V feed on the module, that should also be very close to 0V. If one of those measurements is not 0V, then it will be around 10V (the voltage you are dropping) and you know which side to inspect to find the problem.

Another thing to check which is even easier... Have you measured the 12V output from the module with the sensors plugged in. I.e. is the 12V at the module pin dropping to 2V, same as the sensors? If so, your problem is inside the module and I'd be taking it apart and looking over that circuit board for a bad solder joint, damaged pin or failed component.

[AvenHere]

Took apart the module completely and there is a small piece that is blown lol, buying a new one and going to solder that new piece on if it requires reprogramming. However, 2 pins in the supply for the module read 2.2v which is pretty weird. Harnesses all get 12v then drops to the 2v after one is plugged in.

[AvenHere]

reads 2.2v at the supply for the module, but as stated in another reply the module itself has a burnt corner on the chip. Not sure at this point if its entirely due to the burnt part of the chip, since the supply 12 pin for the module reads 2.2v which is what the front and back harnesses drop to once a sensor is plugged in. (12v without sensor then 2v with sensor in). Weird that the supply for the module is 2.2 but harness output is 12 until a sensor is in. any ideas?

[Avantly]

Can you send a picture? What's the part number of the chip? Chips have a metal lead frame inside the plastic that leads in closer to the silicon die, and then the die is bonded to the lead frame via tiny copper or gold wires (probably copper in this case). Even if a pin corrodes completely off the chip, you may be able to carefully scrape the plastic away from above where that pin enters into the plastic chip package and solder a wire from the lead frame to the board. If it's a commonly available chip that doesn't require any programming then swapping it will be just fine.