E39 Randomly Loses 12v Power

[Ed CT]

146k miles... So it's definitely possible, I just don't want to throw money at the problem. Im not having the weird visor issues like most people. And my logic that the radio lost all power not just the switched turn on means the key switch isn't (the only thing) at fault. Right?

Sent from my Moto Z (2) using Tapatalk

Well, I guess the visor symptom is the most common. When my IgSw went out, it showed itself as a failure in the instrument cluster gages (speedo, tach, mpg gauge) and some odd pixel behavior in the MID display, and there have been other symptoms from other posters, too.

[trevzor4242]

Switches are $15-80 on eBay, about how long is the diy?

Sent from my Moto Z (2) using Tapatalk

[Ed CT]

Switches are $15-80 on eBay, about how long is the diy?

Sent from my Moto Z (2) using Tapatalk

It took me under an hour, and I tend to work slowly and methodically. Make sure you get a quality IgSw. A $15 unit doesn't sound too trustworthy to me.

[JimLev]

Replacing the switch.

IgnSw1.JPG

IgnSw2.JPG

IgnSw3.JPG

IgnSw4.JPG

IgnSw5.JPG

[trevzor4242]

Lost power again and got it on video below:
TLDR - Car lost all electric power suddenly, and i couldn't get to the battery but put a meter on the positive terminal in the engine bay and got a 3v reading. A jult when moving the car caused it to get power again suddenly so I couldn't test more. Meter read 12v on that terminal after it was running again.

https://youtu.be/RDr0bZz0Zws

[Chedley]

Your battery is toast...Recharge it , and/or replace it asap. !! You may also have a connectivity problem to the positive post of the battery.
And no, I do not think you IgSw is the culprit, though it does not hurt to replace it with a new one.

[trevzor4242]

Your battery is toast...Recharge it , and/or replace it asap. !! You may also have a connectivity problem to the positive post of the battery.
And no, I do not think you IgSw is the culprit, though it does not hurt to replace it with a new one.

Why do you think it's the battery? The load tester showed it very healthy. I'm hoping it is but I'm still curious. I also have charged it.

Sent from my Moto Z (2) using Tapatalk

[trevzor4242]

Question: I did some diagnosing the last time it had troubles, and the trunk was closed but I measured 3v at the positive terminal in the engine bay. Where does this terminal get power from? Is it fused, and is it a good reading for the battery?

Sent from my Moto Z (2) using Tapatalk

[trevzor4242]

Since my car is a later model (>1997) it should have a water cooled alternator with a built in VR. Due to this id have to replace the whole thing which is an expensive thing to guess at.

The battery seems to be in great shape and exhibits no obvious signs of failure. Again, possible but an expensive guess.

The ignition switch seems unlikely to me because the radio loses its constant 12v power, not just the turn on wire.

Sent from my Moto Z (2) using Tapatalk

[JimLev]

Yes, you have a water cooled alt, they started those with the 99tu models.
The battery is spliced in 2 places. The first is under the car where the battery cable splits to go to the starter and then along the back pass side of the subframe. From there it follows the subframe over to the drivers side where it splits again to go to the alternator and then up to the top of the valve cover.

You may also want to check the engine ground, it connects to the pass side engine mount and the frame rail. Remove the nut/bolt and clean up the connection.

[trevzor4242]

The battery is spliced in 2 places. The first is under the car where the battery cable splits to go to the starter and then along the back pass side of the subframe. From there it follows the subframe over to the drivers side where it splits again to go to the alternator and then up to the top of the valve cover.

You may also want to check the engine ground, it connects to the pass side engine mount and the frame rail. Remove the nut/bolt and clean up the connection.

Thanks for the continued help, it's very appreciated! I'll check that ground asap and clean it up.

Sent from my Moto Z (2) using Tapatalk

[Chedley]

Why do you think it's the battery? The load tester showed it very healthy. I'm hoping it is but I'm still curious. I also have charged it.

Sent from my Moto Z (2) using Tapatalk

From your diagnostic video posted above in post # 55, your battery reads 12 v (almost empty) when the problem occurs after you gave it a push. The question then is why : a short, or some bad ground connection, or a bad fuse ?? As you seem to have eliminated these as causes, and as your alternator is apparently fine -no battery red light on your dashboard-, I conclude that the battery is bad.

A few winters ago, I had a similar problem with my non-AGM old battery. Did not even think twice: I replaced it with a new AGM battery, and the problem is gone. Though I kept the non-AGM old battery as a backup, and I am not sure if it will give me the same problem if I have to use it...

[trevzor4242]

From your diagnostic video posted above in post # 55, your battery reads 12 v (almost empty) when the problem occurs after you gave it a push. The question then is why : a short, or some bad ground connection, or a bad fuse ?? As you seem to have eliminated these as causes, and as your alternator is apparently fine -no battery red light on your dashboard-, I conclude that the battery is bad.

A few winters ago, I had a similar problem with my non-AGM old battery. Did not even think twice: I replaced it with a new AGM battery, and the problem is gone. Though I kept the non-AGM old battery as a backup, and I am not sure if it will give me the same problem if I have to use it...

I haven't ruled out a bad connection or a fuse, I just haven't been able to find any issue as such in all my searching. I've looked around the battery, under both the driver and passenger carpet, and around the engine bay. Not dismissing it as a possibility, I just can't find the issue.

Even though it's charging could my vr still be bad with no light on the dash?



Sent from my Moto Z (2) using Tapatalk

[JimLev]

Even though it's charging could my vr still be bad with no light on the dash?

Most likely no. When the VR craps out the alt isn't charging so the battery light in the cluster will come on.
Go to HF (about 24 miles from you I think) and get one of these, the socket is always powered so that will narrow down where the problem is.
https://www.harborfreight.com/12-vol...ter-66842.html

[trevzor4242]

I've noticed that issue seems to happen as I'm coming to stops, and especially in stop and go traffic. I've been watching voltage and the battery does seem to sit too low when the cars off at 12.5v or less. When cruising it runs at 13.5-13.7v and will drop down to low 12s for a few seconds upon coming to a stop. Even if the battery is not the cause of my issues it looks like it's time to replace it. It is however an AGM battery, specifically a duracell SLI49AGM

[JimLev]

At idle the alt really isn't putting out much juice. 13.5 to 13.7v shows you alt is working fine.
When my alt died my engine kept running (to get be almost home) until the voltage got below 11 volts, then it died.

Turn on the headlights for 1 min and see what the voltage drops down to. If it's below 12v the battery isn't capable of holding a charge.

[trevzor4242]

At idle the alt really isn't putting out much juice. 13.5 to 13.7v shows you alt is working fine.
When my alt died my engine kept running (to get be almost home) until the voltage got below 11 volts, then it died.

Turn on the headlights for 1 min and see what the voltage drops down to. If it's below 12v the battery isn't capable of holding a charge.

To clarify the 13.5-13.7v is while moving not at idle.

Sent from my Moto Z (2) using Tapatalk

[JimLev]

To clarify the 13.5-13.7v is while moving not at idle.

Sent from my Moto Z (2) using Tapatalk

Yes, while driving.

[trevzor4242]

Voltage dropped from 13.5v to 12v within a minute and then stayed at 12v for about 7 minutes til I pulled the meter off. This is with brights on, and I have a video if it helps.

Sent from my Moto Z (2) using Tapatalk

[JimLev]

Voltage dropped from 13.5v to 12v within a minute and then stayed at 12v for about 7 minutes til I pulled the meter off. This is with brights on, and I have a video if it helps.

Sent from my Moto Z (2) using Tapatalk

That's with the engine off, correct?
If you had the brights on for 7 min with the voltage staying at 12v then I'd say the battery isn't the cause of the car shutting off.
The battery may not be at 75%, but it should be good enough to last for a while.

[trevzor4242]

That's with the engine off, correct?
If you had the brights on for 7 min with the voltage staying at 12v then I'd say the battery isn't the cause of the car shutting off.
The battery may not be at 75%, but it should be good enough to last for a while.

Yes engine off.

I'm at a loss. Alternator/vr seems unlikely according to your accounts of usually complete failure, battery seems unlikely cause it holds enough charge (certainly enough to not be at 3v), ignition switch is possible but again doesn't explain the radio losing its constant 12v, and I have yet to find any shorts or bad connections. What should I do?!

Sent from my Moto Z (2) using Tapatalk

[mattmar1]

if you can get the 3vdc at the jump point to repeat, try reading voltage to as many ground points as you can get your probe on. might even try running a piece of wire to the battery negative post. if you find a 12v reading to the jump point at any one of them, its a grounding problem.

[trevzor4242]

if you can get the 3vdc at the jump point to repeat, try reading voltage to as many ground points as you can get your probe on. might even try running a piece of wire to the battery negative post. if you find a 12v reading to the jump point at any one of them, its a grounding problem.

I'm hoping for the issue to arise again while I'm home but that might not happen. On second thought I'm gonna throw my multimeter in the car. Next time it stalls if it's safe I'll keep it there and do as much testing as I can including your idea. Wish I could get to the battery with no power but the trunk wouldn't be openable so I can only test grounds from the engine bay.

Sent from my Moto Z (2) using Tapatalk

[JimLev]

Open the trunk with the KEY!

Have you checked the ground cable from the engine support bracket to the frame rail?

[trevzor4242]

Open the trunk with the KEY!

Have you checked the ground cable from the engine support bracket to the frame rail?

About that... My lock is messed up so I can't and no I haven't checked that ground yet but thanks for the reminder

Sent from my Moto Z (2) using Tapatalk