E70 X5 4.8 Electrical Maladies
 

Afternoon all. After a couple of years out I'm back in the land of X5 ownership, this time an E70 and a 2007 4.8 !

Picked her up from Auction, my delivery plater had to get her jumped. Then went to fill and couldn't restart, the AA reckoned it was a bad Alternator, so she was flat bedded back. However since been started don the button with no issues, and my mechanic recons its a lazy Alternator, but not dead ( giving out 12.8 or so when warm).

However think I may have a few bugs and I know my old E53 was sensitive to voltage drop.

Had her valeted by one of the lads who works for me, when she came back clock was reset to zero and MPG also ( was also like this when I got her).

Am wondering if anyone has any experience of this before I plumb for a new alternator, which at £400 is not the cheap option !

Cheers all

Interesting, I have been logging voltage and temps while commuting. My voltage right after startup drops to 11.8 then after 5 seconds or so settles down on 14.1. Once warmed up she sits pretty steady at 13.9 regardless of load (all lights one and AC or no lights and HVAC off). Seems like 12.8 is a little low, what is the voltage of the battery with engine off? Hopefully others with more experience will chime in.

Your symptoms are similar to those I experienced a few years ago with my 2010 X5 35D. Mine were caused by a very corroded engine to chassis ground strap.

I didn't have a problem jump starting the engine because I would ground the jumper cable to the engine ground. The other electronics didn't use enough current to make the voltage drop across the bad ground strap high enough to cause issues.

Measuring the resistance between the engine and chassis with a DMM will confirm if this is your issue. The resistance should be well below 1 ohm.

Happy troubleshooting!

Alternator, regulator, IBS cable, ground strap.

Off the top of my head, thats the list....