schnitzelfire

Hello,

I am wondering if anyone has any experience diagnosing these issues.
I do not have STAR diagnostic unfortunately (although I should have it), so I cannot be 100% sure but I thought I had found the root of the problem.


I have changed the Aux Battery Relay and the Aux battery but I still get the error. I get 14V to pin 30 of the relay so fuse 32 is good. I also get 14V to the rear battery so my alternator is functioning correctly. Continuity is good from positive of battery to pin 30 of relay.
How would I go about verifying the part that is highlighted in yellow?
I know where the polyswitch fuse is located but how do you verify its continuity? I cant seem to access the fuse part (its right next to the aux battery).
To what pins do the relay activation go to the BCM?
Should I bring my car to a garage where they have access to STAR diagnostic?

Thanks to anyone who can help me!

CaliBenzDriver

Have you made progress? Perhaps I can help.

The circuit you've highlighted YLW is the control side of your AUX relay. It lets the BCM open/close the contact to connect AUX.
The parts you've replaced already were good wear item.


Now as to why AUX is still acting up...
1- Check BCM *GND* is good & clean.

2- CAN-B is the widest and serves the most modules.
Check its not disrupted by a bad module.

3- Is the BCM defective?
- Are you able to read it over Can-B?
- Open it to have look inside...