Fault codes about battery voltage and air quality sensor

[46lukasz]

Hello,

I have 4 fault codes in my 2016 A5 2.0 TDI that keep coming back periodically after clearing.
I am scanning using OBDeleven so may not be as accurate as VCDS but here is the information

The car is running fine and they don't really affect me but i would like them to not be there.

1. Battery monitoring control module
   No signal/communication
   Fault code 00458
   Static
   166220 km
   2022-03-11 7:55:31
   
   
2. Voltage stabilizer
   No signal/communication
   Fault code 03705
   Static
   166220 km
   2022-03-11 7:55:31
   
   
   
   I think these two are related because of the time stamp and nature of fault. I have the start stop/system turned off, the battery was not changed recently, the car has no issues starting even after sitting for about a week. The battery was disconnected for a short time when I was changing the steering wheel to a flat bottom one a while back. But this fault came up some time after that so not sure if that's related. Any ideas what can cause it or what i can check or measure to diagnose?
   
   
   
3. Humidity sensor in fresh air intake duct
   Faulty
   Fault code 03608
   Intermittent
   166450 km
   2022-03-13 18:17:07
   
   
4. Vehicle Electrical System Control Module
   Please read DTC
   Fault code 00457
   Intermittent
   166450 km
   2022-03-13 18:17:03
   
   
   
   I think these two are also related because of the time stamp and nature of fault. They are intermittent and if the sensor in question is the one attached to the cabin air intake next to the brake fluid reservoir, then I think its not really that serious, but i would like to have it gone. I could buy a new sensor but will that fix the issue or can it be something else?

Hoping that someone came across these already and can shed some light on it
Lukasz

 

[46lukasz]

I had a look at this problem today. It turns out that what DrGER from A5OC forum linked to me was exactly what happened in my case as well when it comes to the first 2 faults.

VCDS - 61 Battery Regulator - No response from controller

www.a5oc.com

I had no live data in channels 18, 19, 20 of the gateway.
There were no errors when connecting to those channels in order to read them, but nothing was reported in them.

Here are some pictures of my work in case someone comes across the same issue. But there are already plenty of pictures in the link above by DrGER

The loom with the issue runs below the air vent cover in the right side of the boot.
First the fusebox needs to be unbolted (just one bolt) and set to the side.
The air vent cover needs to be removed too. I gave it a good pull and it came off.
Make sure to pull it straight out and not at an angle or you might break some tabs.
The loom is held in place by 4 pieces of tape that have to be cut. It can be then re-attached using zip-ties.

Then the tape covering the loom can be undone, and the offending crimp can be found right under the air vent.
The second I touched the insulating bubble around the crimp, it came right off and the wires were already disconnected inside it.
It was full of corrosion. I then stripped the wires, twisted them together and soldered + crimped + applied a few layers of heat-shrink.

There is a second insulating bubble there with some thick wires crimped together. I suspect they are power wires.
The bubble is see through but it didn't seem like it was corroding, maybe some slight crust on the edge, so I left it alone.

Then I wrapped the loom in new tape and attached to the mounting plates with zip-ties. Then I put the fusebox back in and it was done.

The live data channels began displaying information right away so the job was a success.

I can only assume there was corrosion there because of the air vent and possible humidity getting in through it.
I didn't find any water there and the foam wasn't damp anywhere so that's a good sign.

Lukasz

 

[pelhamsdetailing]

Good on you mate. Glad you got it sorted out.