Auxillary battery issue

[nacimroc]

Last November a load of errors popped up (EV system/ACS/RBS filures). I narrowed the problem to low voltage on the Auxillary battery thanks to posts from the clever people here. I replaced with it a proper (expensive!) AGM battery and all the errors went away for a few months. Problem occured again about 2 months ago. Checked voltage and battery was at 12.6v. We use the car a few times a week including long journeys and its working fine even though these faults pop up a few minutes into every journey.

I'm really confused as to what the issue could be?

Only works ever done were, I had a guy change the factory 20 pin trailer lights to 7 pin so suspected a short or parasitic load, but it has never died completely. Then I read about some ABS sensor on a wheel hub that could be a cause. I'm really at my wits end.

 

[AndyInOz]

If you live somewhere that underbody rust is an issue, you could have a grounding strap somewhere that is corroding away. (Modern cars typically have many).

Best to get under the car and inspect all of them.

Hopefully other members can let you know the location of the straps.

 

[nacimroc]

Thanks. Will give it a look. Going to inspect trailer wiring this weekend so will examine this.