Jonny G

Update - solved the issue. Upon reading other threads I checked the ABS wheels speed sensors on all 4 corners. The front passengers side sensor was damaged. A break in the sensor case was letting water into it. I’ve replaced the sensor and the faults have all gone away. It was a bit of a pig to change as it’d melted into the bearing housing. Quite a coincidence that the wheel bearing was changed by the garage a few weeks before all these faults started appearing.

Thanks yes, saw that thread. It seems a common issue with the C7, they like to let water in as much as possible. Further investigation this evening and I narrowed down the leak. See the picture attached, but the leak is coming through a seam in the side wall. Circled the area in red. I have sealed this area with Gorilla waterproof patch & seal tape. I removed the Voltage stabiliser unit to dry it out, and also moved the wiring loom for the Voltage Stabiliser unit up and back out of the spare wheel well up into the area where the main fuse board unit is. I hope that these two actions will cure the problem.

My joy has been short lived. The car is fine when driving in the dry, but today in the rain, all the faults have returned. I spent an age trying to seal any and all holes in the spare wheel compartment of the car where I keep finding moisture, but I keep finding moisture in the bottom and a damp patch on the carpet, drivers side under the spare wheel, below the Bose sub woofer. Does anyone else have any suggestions?

Like others on the thread, I’m beginning to think that this is all due to moisture. On further investigation, I found that the carpet in the boot was soaking, as was the boot floor. Stripped it all out and dried everything off in the sun. I’ve sealed all the rubber plugs and dried the Voltage stabiliser unit. I’m hoping that this will solve the problem.

Post update. I tested the alternator yesterday. With the engine off the voltage on the battery (new) was 12.5v, then on starting the voltage dips but at 2,000rpm and above the voltage increase to 13.6v. Not as high as I thought it would be but that does suggest it is charging the battery. I checked the belt to see if it was worn or loose, but it seems good, no visible signs of damage or wear, and it was tight. Put the battery on the trickle charger overnight and the warning lights were not there this morning. I guess the next thing would be parasitic drain. I unplugged the only 2 accessories in the car when I parked and turned the car off, the Nextbase dashcam and the quadlock phone charger. Hopefully this will solve the issue. Do you think repeatedly only doing short journeys, and driving in economy mode where rpm is always low contribute to the issue? I’ve had the car from new and this problem only surfaced in December 23.

The new battery is a Varta (as was the old). I checked and made sure I was getting the OEM replacement. I’ll check the alternator. The car has only done 56k miles, the alternator should last longer than that shouldn’t it? I though they normally last 80k to 100k?

Thanks Gareth. I haven’t actually check the alternator, I’d assumed due to the age and low mileage that the alternator would have been ok, but I will now check it out. The large number of totally unrelated faults, ESC, air suspension, brake servo, electric parking brake, ABS, high beam assist, and more all seemed to point to the low voltage problem, and as the battery was still the original I thought (hoped) changing it would be the end of the problem but no, it’s back. I’ll post once checked.

I’m having the same issues with my A6 C7 Allroad. Multiple faults and warning lights. I recharged the battery, which seemed to cure the issue for a while, but when it came back I decided to replace the battery as it was 6 years old. However, a 2 months on and the problem has returned. New battery, all coded to the car and installed, and one cold morning the issues have returned. Interesting to hear that it could be related to moisture in the car as I recently noticed that the panoramic roof had been leaking (in the common way that they do!) but I’d solved this. I wonder if the battery issue is due to residual moisture still in the car? I did notice moisture under the spare wheel.