Error only when it drop below about 11v steady. Basically when it completely fails.

Look into your alternator and if you can replace the VR on it. Much cheaper than whole alternator

Eh. Kinda throwing the towel on this. VR is cheap but it's got more issues that I'm just throwing in the towel. I guess this is one of them but the main shitlist is the Valley Pan. It started with a small loss and almost after every trip these days, I'm popping the hood. Sometimes it needs 3 oz top off. Sometimes 12-14 oz top off. It's so varied on how much loss between each drive session but it's to the point where even buying coolant is questionable :rofl:

The previous alt. repair requirement was WILD. If memory recalls, it literally just lit up like a Xmas tree on a Red Light Stop. Thankfully someone helped to push it to the side on a Hot Summer Day

It's common with alt failure and e53 that you'll get trifecta if voltage momentarily drops below about 11.5. Even if the voltage recovers no sbs/dsc until you restart

Did someone say Brembo!?

Would love to upgrade the brakes on my X5, but they probably wouldn’t fit the 16” wheels I’ve got though.

Going back to the original topic I’ve had my motorhome battery on for the last few days. It certainly turns over more quickly than the one I took off.
Yesterday I received the new FSR in the post so I half heartedly started to install it. Couldn’t really be bothered so gave up after a while but I did notice that there was no fan noise at all from behind the console - normally it is quite evident. I’ll get round to fitting it soon I guess.
At the moment I have a spare battery and jump leads in the back just in case as I’m doing a lot of longer journeys over the next few weeks.
I probably should buy a small portable booster pack..

I would pull up the voltage in the dash while driving. Unlike the E70, the E53 doesn't turn the alternator on and off during normal use so should stay at 14 ± 0.4 and usually won't change more than ±0.2 from it's baseline.

Be curious as I have asked in the past - what readings do you see in the cluster when healthy

I've never looked at it when everything is **healthy** to see what the cluster shows....
I presume there is some V loss after modules or no, it should be 14 on average

On my E53 the voltage was 13.8 ± .2 no matter the rpm.

The trunk unlock usually happens from water ingress. I pulled the rubber button off mine when that happened and never replaced it. Worked until the car was killed by a deer