2000 740iL electrical issue

[DaddyGlenn]

Here is the progression of symptoms:

A couple months ago it started with the monitor in the dash intermittently would go screwy or stop updating (time). The frequency of this issue increased. The radio got into the act as well. It would randomly stop producing sound. But if I hit the radio power button twice, off then on, it would come back on. The frequency of this increased to where it was only 2-3 minutes between power cycles. By this time, the monitor in the dash would only show a static filled glow.

Its been that way for a couple weeks and then a couple days ago, the battery light would come on intermittently. Yesterday, it came on and stayed on. Then on a short trip today, the transmission went into limp mode and several other warning lights came on, including the air bag light. So after limping home it now has a dead battery.

Battery is only a year or two old. I've got it on a battery charger now so I can try to get it running so I can take it to the shop.

Wondering if this sounds like a slow failure of the alternator gradually causing various electrical systems to fail as the output decreases.

Anyone?

[DaddyGlenn]

Sat on the battery charger for a while and then started right up. Still have the battery light on and the issues with the screen and radio but no transmission limp mode. Off to the shop in the AM.

[DaddyGlenn]

Local general purpose shop couldn't diagnose it. They suggested an auto electric specialty shop, but after hearing about the details, he wouldn't touch it. So we limped it to the Dealer. Good thing is we got a 2015 320i for a loaner.

Now we wait.

[DaddyGlenn]

Dealer has invested a good chunk of time into it but still have not isolated the issue.

[DaddyGlenn]

Dealer called today. Alternator and battery. Alternator went bad and toasted the battery, too. $1,700 to fix. Yes, I could do those myself but I really don't have the time and want to have someone other than myself to yell at if problems continue.

Also having them replace the rear springs too.

[DaddyGlenn]

All fixed. Very interesting symptoms for a failing alternator.

[DaddyGlenn]

Well...... not all fixed. Turns out there were multiple issues. The display going blank and radio shutting down have returned.

After much research, I found that this particular set of symptoms usually means a bad navigation unit. The Nav unit controls the display. Every two to three minutes a scan is run and when the Nav unit throws an error, things are shut down, namely the radio and screen. You can get the radio back on by hitting the power button twice (off then on) but it will only last until the scan runs again. Wash, rinse, repeat. ....

The solution is usually to replace the Nav unit. So instead of additional troubleshooting to confirm the bad navigation unit, I am taking the opportunity to upgrade to a MK IV unit. Found one on ebay for $400 shipped including the DVD. When it arrives, I will document the upgrade in another thread.

[JTL]

I had some weird electrical issues a couple of years ago with the radio and interior lights etc on my -98 E38. There were some Bimmerboard threads on how a failing ignition switch could be the cause. I changed out the electrical part of the switch and all problems were gone. It wasn't too bad of the job either. There should be a write-up on how to do this on e38.org.

[DaddyGlenn]

Installed a MKIV Navigation unit and all is well. No more electrical issues and navigation is better/faster.