[ProfessorCook]

Now I have to warn everybody that messing about with an electrical system has its inherent risks and if you accidentally or intentionally connect things in the wrong way, you can really muck up the works. In addition to, perhaps, frying the electrical system or wrecking really, really expensive computer parts which you might not be able to replace anytime soon, there's a physical risk of hurting yourself by electrocution, burns, or even an explosion if there is hydrogen gas lurking about the 12V battery. Ok? Don't faff about here unless you're confident in what you're doing.

 

[ProfessorCook]

Ok... the fuse box first.

There's a small plastic cover (red ellipse) with a single locking tab (green ellipse). Press the tab in with your finger and the small cover is easy to remove.

Removing the cover exposes a positive 12V terminal. (I measured 12.87 volts with the car "off" when referenced to the negative terminal of the battery.)

There then are 3 more tabs (red circles) that are easy to press in to remove the fuse box cover.

 

[ProfessorCook]

Ok... now the 12V battery.

There's a cover over the battery that has two hinged flaps. The forward flap has a first-aid cross on it. By lifting the tab, you can lift this up to expose the connection between the 12V battery and the other cables connected to it.

When I first posted this thread, I said that If I were to disconnect the car from the 12V battery, this would be where I would do it. Since that time, multiple forum members have said that it's better and safer to disconnect the negative terminal. So don't disconnect this at all, but if you insist (perhaps to change the battery), don't disconnect this until you disconnect the negative terminal. More on that later.

 

[ProfessorCook]

There's a second hinged cover that's a little harder to open. The plastic latches are designed to be pried back with a rather small, flat-blade screwdriver. You insert the blade into the lip and then fulcrum the screwdriver gently back to pull the loop out from under the hook.

There are two of these. The obvious one shown here, and another around the back. I find a good headlamp to be a most valuable tool and this is a place where it really comes in handy. Pull that second tab, and this cover hinges up to expose wires that need to be hot (connected to positive 12 volts) all the time.

 

[ProfessorCook]

At this point, if you open both flaps and then one of two remaining tabs around the back, you can lift off the entire piece which exposes some high amperage fuses below.

You can see a "mega" 175 amp fuse, a 125, 100, and 60 amp fuse here. There's also a 15 amp fuse off to the side.

 

[ProfessorCook]

And, of course, near the back, is the connection to the negative terminal of the battery (red ellipse).

This is where multiple forum members have assured me that it's best to disconnect the battery if you're going to do a 12V disconnect. Note that it's not under covers and the nut is angled for easier removal. If you loosen the angled nut, you should be able to carefully lift the connector off the negative stud and then insert some substantial insulating material between to make sure no connection will inadvertently occur.

 

[ProfessorCook]

Now I didn't want to disconnect my 12V battery and I have no training or reliable information from other sources as to how best to do this. That being said, forum members have assured me that the way to do that is to disconnect the negative terminal first. If, for some reason, after disconnecting the negative terminal, you still need to disconnect the positive terminal, I think I would first remove the two fasteners (green circles) that hold the plastic panel and cover to the battery, and then I'd remove the nut that makes the connection to the fuse panel (red circle). From what I can see and after probing around a bit, I think this would allow me to lift the metal fuse panel off the threaded stud thus disconnecting the 12V battery from the car.

 

[ProfessorCook]

I was 21 years old messing about with my first car... a used 1974 AMC Ambassador station wagon... to install my own after-market stereo system (cassette tape player deck!!) when I discovered something about cars and electricity. You can touch a 12V terminal with your hand and not get shocked. 12V isn't much incentive to force electricity through your body so as you'd notice. But if you happen to connect a 12V battery to ground with something like a screwdriver, you realize it's not good. There is buzzing and flame and heat and arcing and welding and smoke and... well... it's very bad indeed.

So... once again, I am compelled to warn everybody who bounces across this thread that things can go wrong very quickly when you're playing with electricity. You could wreck your car and you could wreck yourself. So please don't try anything based on the information I've posted here. Find good, reliable information from Polestar or Volvo or a trusted mechanic. Then go double-check everything. OK?

 

[ProfessorCook]

Very good walkthrough to bookmark for the future. As for resetting the car via the 12 V, I would pull out the negative terminal only, wait a minute or so, then put it back on. Don't think we should pull the positive first.

Yeah, that should work as well, I'd guess. Do you think it's easier/safer to do it that way?

 

[ProfessorCook]

I would even go so far as to recommend that @ProfessorCook modify or remove his recommendations as to how to disconnect the battery. There is a risk that an otherwise very nice guide gets improperly used potentially for years to come.

'Very good idea, sir. Thank you. I have edited the previous posts. If you get a chance, I'd appreciate you having a look at them to see if you think I've made things better and clear now.

 

[ProfessorCook]

Good news, bad news:

Good news - disconnecting the negative terminal is totally easy. I managed to do it just now and not electrocute myself.


Ah well.... 1.5 weeks to go until my service appt....

Well... At least you gave it a shot and we all know now how to do it.

Good luck with the rest.

 

[ProfessorCook]

Unfortunately a 12v reset is unlikely to fix your issue as the TCAM has it's own battery backup. I think a factory reset of TCAM is what the workshop will be doing for you.

I wonder if that's as easy as pulling the correct fuse... But no. The fuse boxes are powered by the 12 volt battery, I think. So if disconnecting the battery doesn't work and it has its own battery...

I tried to remove the rear headliner when I installed my dash cam. It seemed glued in place. So I don't think it's easy to get in under the fin. But I suppose there has to be a way.

 

[ProfessorCook]

Even if you get to the fin, the battery is inside, so far as i'm aware it's not possible to disconnect the backup battery, it has to be reset by software access.

Also, the headliner shouldn't be glued in, it will be clips... you're probably not pulling in the right direction or hard enough, or both.

'Makes sense.

I was surprised by what I experienced with the headliner. You're probably right about it, but I'll let someone else have a run at it.

 

[ProfessorCook]

Are you sure that battery is in the fin itself? I thought I had read somewhere that it is in one of the C-pillars, and accessible by removing a cover.

I'm not at all sure.

 

[ProfessorCook]

Damn it!

You must be frustrated.

Going to try to jump it?