Audi A4 B8.5 parking assist / reversing sensors stopped working

[Tiger-G]

Just a quick how to, as I couldn't find much info online when my parking assist screen stopped working:

As I couldn't find much info online as to why my parking assist screen stopped working I ran a VCDS scan which came back:

02070 - rear parking aid sensors. 011 - open circuit
01545 - sensor parking aid left rear (G203). 009 open or short to ground.
01546 - sensor parking aid mid left rear (G204). 009 open or short to ground.
01547 - sensor parking aid mid right rear (G205). 009 open or short to ground.
01548 - sensor parking aid right rear (G206). 009 open or short to ground.

Checking with Ross-Tech the codes it pointed to:

Possible Symptoms​

• Parking Aid not working

Possible Causes​

• Main Connector to Rear Sensors disconnected
• Separate Connectors to all Rear Sensors disconnected
• Wiring/Connector(s) from/to Rear Sensors faulty

Possible Solutions​

• Check Main Connector to Rear Sensors
• Check Separate Connectors to all Rear Sensors
• Check Wiring/Connector(s) from/to Rear Sensors

Then purely by accident I came across this Audi Technical service Bulletin:

(first on the page in link, if it works ?? If not search: Audi tech service bulletin rear parking aid sensors wiring fault code 02070)

technical buttetin audi reversing sensor wiring - Google Search

It shows diagrams of exactly what I found my issue to be:

After removing the rear bumper (that was fun...not) to gain access to the parking sensor wiring loom, I removed the cloth tape at the splice to find this:

The spliced wire that goes to all four parking sensors had corroded and snapped. This is purely down to bad design by Audi. First of all, they have the wiring loom exiting the inner bodywork right at the bottom where moisture and water collects. And secondly, and more importantly, the cloth tape they use to bind the wiring as very absorbent, and acts like a sponge to suck up and direct all the moisture to this splice !! Well done Audi, you've excelled there !! NOT !!

So I soldered an extension wire in (don't judge, the stuff I had to do it with was poor) and checked for continuity with a multimeter, and everything checked out ok.

I put the rear bumper back on and checked if the parking sensors were working, and unfortunately, they weren't. I'd had enough by then and just wanted the car back on the road. I ran a VCDS scan and cleared all the fault codes, but the parking assist screen still didn't come on and it was greyed out on the screen. Gutted.

Anyway, I ran the car for a bit, as the battery was quite flat, and hey presto, for some magical reason, the park assist screen and all relevant warnings started working again !! Result !!

Hope this helps someone in the future, as I struggled to find enough info to help

 

[NHN]

Similar thing happens on some front sensors on A7's, the bumper & loom are positioned so the wires get chopped by the bumper fitting, it's idiotic tbh.

 

[spartacus 68]

Well done Tiger-G, good write up. Of course Audi could have used tinned wiring to resist corrosion at this particular part of the loom, but that would have cost more.

 

[NHN]

It's more like it's been stretched, snapped & thus resulting situation from water on open wires, it's a stress point where it enters the car, worked on plenty to know that location, it doesn't look like it's due to water ingress, just tight wires, we're talking 0.35 to 0.5 wires that are thin wall anyway.

 

[Tiger-G]

Well done Tiger-G, good write up. Of course Audi could have used tinned wiring to resist corrosion at this particular part of the loom, but that would have cost more.

Cheers .

I always appreciate it when people on here take the time to give me advice, so on the very limited times I can hopefully do the same, I'm only happy to contribute.

 

[Tiger-G]

It's more like it's been stretched, snapped & thus resulting situation from water on open wires, it's a stress point where it enters the car, worked on plenty to know that location, it doesn't look like it's due to water ingress, just tight wires, we're talking 0.35 to 0.5 wires that are thin wall anyway.

Possibly, but with the greatest of respect, the cloth binding tape was damp, and the separate cloth binding tape where the wires are spliced was soaking wet. When I unfolded the splice tape, as you can hopefully see from the pic, everything just crumbled to bits. In my opinion, it's caused by the cloth tape absorbing water in the rear back quarter of the car and that water being directed to the spliced cloth tape which acts as a sponge. This corrodes the spliced wires and the insulation breaks down. It basically says that too in the technical service bulletin. There's plenty of slack in the wiring loom for it not to be under any stress, but if you're working on them all the time, you'll know more than me

Here's a couple of screen shots from the TSB, that shows the same issue I had: