E46 M3 Losing All Electrical Power / No Start

[Marc E46M3]

Hey guys, hoping to get some input before I start replacing parts.

2004 E46 M3. The car recently started having some strange electrical issues. Yesterday it shut off on its own and I lost all electrical power. No crank, no dash, nothing.

AAA came out and was able to jump-start it. I drove it about 10 miles home without any problems. Pulled into the garage, shut the car off normally, and immediately afterward it was completely dead again.

Before this happened, I scanned the car with my Foxwell and found these DSC codes:

5D97 - DSC sensor voltage supply
5DF4 - System voltage <9 volts
5E21 - Pressure sensor 2

The first two showed "not present," but the system voltage below 9 volts definitely caught my attention.

Another possible factor is that I had a new stereo system installed on July 15. Xtrons head unit, Match DSP/amp, separate Match sub amp, Helix 10" sub, and new power wiring.

The DSC/brake lights aren't new. They've been coming on intermittently since I installed aftermarket wheels and suspension, so that may be a separate issue.

I'm thinking battery, alternator/voltage regulator, bad power or ground connection, or possibly something related to the stereo install.

Any thoughts or guidance definitely appreciated!

[elrichmeister]

First thing to check is the voltage on the battery. Should be more than 12v cold, and more than 13-14v running.
If battery voltage is really low then its likely the cause of not starting and other electrical issues.
That would be the first thing to check.

[sapote]

I'm thinking battery, alternator/voltage regulator, bad power or ground connection, or possibly something related to the stereo install.

.

charge up the batt or have it jumpped to run the engine, while idling measure voltage at the batt POSTS, then at fender jumper posts. Let it idling or drive it for 10 minites, shut down, wait for 10 minutes, and measure voltage at batt. Report back.

[Marc E46M3]

First thing to check is the voltage on the battery. Should be more than 12v cold, and more than 13-14v running.
If battery voltage is really low then its likely the cause of not starting and other electrical issues.
That would be the first thing to check.

Thanks, man. I'll need to order a multimeter and will report back. Appreciate you sharing some guidance.

[Marc E46M3]

.

charge up the batt or have it jumpped to run the engine, while idling measure voltage at the batt POSTS, then at fender jumper posts. Let it idling or drive it for 10 minites, shut down, wait for 10 minutes, and measure voltage at batt. Report back.

Thanks for the advice, dude. I will tinker around with this weekend and will report back. Appreciate you.

[Marc E46M3]

.

charge up the batt or have it jumpped to run the engine, while idling measure voltage at the batt POSTS, then at fender jumper posts. Let it idling or drive it for 10 minites, shut down, wait for 10 minutes, and measure voltage at batt. Report back.

Update from testing tonight:

Bought a Klein MM325 multimeter and did some basic battery/charging tests.

Battery voltage with car off before starting: 12.25V

Checked directly at battery posts and cable clamps: 12.25V

Checked voltage at the under-hood positive jump terminal: 12.24V

Car started normally tonight, without having to jump (which I found odd)

Engine idling: 13.95V

Engine idling with headlights, HVAC blower on high and rear defroster on: 13.72V

Accessories back off, engine idling: 13.95V

Shut the car off, waited about 5 minutes: 12.61V

So at least during tonight's testing, the alternator appears to be charging and the battery is accepting a charge.

This is after the car previously shut off while driving, became completely dead, needed a jump from AAA, then drove about 10 miles home and was completely dead again immediately after shutting it off.

I've also previously had stored low-voltage faults, including DSC 5DF4 for system voltage below 9V.

At this point I'm wondering if I'm dealing with an intermittent alternator/regulator issue, battery issue, intermittent power/ground connection, or possibly a parasitic draw.

I'm going to let it sit overnight and check battery voltage again before opening the doors or turning the ignition on.

Curious what you guys think based on these numbers.

[Marc E46M3]

First thing to check is the voltage on the battery. Should be more than 12v cold, and more than 13-14v running.
If battery voltage is really low then its likely the cause of not starting and other electrical issues.
That would be the first thing to check.

Update from testing tonight:

Bought a Klein MM325 multimeter and did some basic battery/charging tests.

Battery voltage with car off before starting: 12.25V

Checked directly at battery posts and cable clamps: 12.25V

Checked voltage at the under-hood positive jump terminal: 12.24V

Car started normally tonight, without having to jump (which I found odd)

Engine idling: 13.95V

Engine idling with headlights, HVAC blower on high and rear defroster on: 13.72V

Accessories back off, engine idling: 13.95V

Shut the car off, waited about 5 minutes: 12.61V

So at least during tonight's testing, the alternator appears to be charging and the battery is accepting a charge.

This is after the car previously shut off while driving, became completely dead, needed a jump from AAA, then drove about 10 miles home and was completely dead again immediately after shutting it off.

I've also previously had stored low-voltage faults, including DSC 5DF4 for system voltage below 9V.

At this point I'm wondering if I'm dealing with an intermittent alternator/regulator issue, battery issue, intermittent power/ground connection, or possibly a parasitic draw.

I'm going to let it sit overnight and check battery voltage again before opening the doors or turning the ignition on.

Curious what you guys think based on these numbers.

[sapote]

Battery voltage with car off before starting: 12.25V

Engine idling: 13.95V

At this point I'm wondering if I'm dealing with an intermittent alternator/regulator issue, battery issue, intermittent power/ground connection, or possibly a parasitic draw.

12.25v engine off is too low. but this should not cause engine shut off while driving if alternator is good with 13.95v charging volt.
Parasitic drain cannot cause engine shut off while driving with good alt.

I would use the dash hidden display to display the batt voltage while driving to see at any moment the voltage drops down below 13v.
before the car shut off during driving, did the dash show any odd behavior (that relate to a low batt volt)?

[elrichmeister]

I agree with Sapote with 12.25v is a bit low. I would monitor the voltages before every cold start and if a lower voltage causes starting issues.
I would try to at least get a full charge on the battery and see if there are less issues with higher average battery voltage.

[uberchris]

Have you checked the connections to the battery? The stereo installers probably disconnected the negative when doing their work. Maybe they didn't tighten it down?

[Marc E46M3]

Have you checked the connections to the battery? The stereo installers probably disconnected the negative when doing their work. Maybe they didn't tighten it down?

Yes, sir. I checked the battery connections and everything feels tight and right.

[Marc E46M3]

12.25v engine off is too low. but this should not cause engine shut off while driving if alternator is good with 13.95v charging volt.
Parasitic drain cannot cause engine shut off while driving with good alt.

I would use the dash hidden display to display the batt voltage while driving to see at any moment the voltage drops down below 13v.
before the car shut off during driving, did the dash show any odd behavior (that relate to a low batt volt)?

I had no idea there was a hidden dash display lol, and I have yet to try it. I don't drive the car much - have put on roughly 5K miles over the past 5 years. During this period, I have noticed the DSC and brake lights come on and off intermittently. I suspect that it's related to the recent issue, but I'm not certain.

[Marc E46M3]

Update from testing tonight:

Bought a Klein MM325 multimeter and did some basic battery/charging tests.

Battery voltage with car off before starting: 12.25V

Checked directly at battery posts and cable clamps: 12.25V

Checked voltage at the under-hood positive jump terminal: 12.24V

Car started normally tonight, without having to jump (which I found odd)

Engine idling: 13.95V

Engine idling with headlights, HVAC blower on high and rear defroster on: 13.72V

Accessories back off, engine idling: 13.95V

Shut the car off, waited about 5 minutes: 12.61V

So at least during tonight's testing, the alternator appears to be charging and the battery is accepting a charge.

This is after the car previously shut off while driving, became completely dead, needed a jump from AAA, then drove about 10 miles home and was completely dead again immediately after shutting it off.

I've also previously had stored low-voltage faults, including DSC 5DF4 for system voltage below 9V.

At this point I'm wondering if I'm dealing with an intermittent alternator/regulator issue, battery issue, intermittent power/ground connection, or possibly a parasitic draw.

I'm going to let it sit overnight and check battery voltage again before opening the doors or turning the ignition on.

Curious what you guys think based on these numbers.

Here is an update from today's recent testing.

The car had been sitting since the last round of testing. Before starting it today, the battery measured 12.12V. I checked it again and got 12.18V.

Started the car normally and measured 13.75V at idle.

Then I turned on the headlights, HVAC blower on high, and rear defroster, with the stereo off. Voltage initially bounced around 13.45V, then dropped to 13.25V, 13.19V, and eventually hovered around 12.72V. The lowest reading I saw was about 12.55V.

With just the rear defroster turned off, voltage came back up to around 13.25V.

Turned all the loads off and it went right back to 13.75V at idle.

Let it run a few more minutes, shut the car off, waited about 2 minutes and measured 12.57V at the battery.

So the alternator is definitely charging, but it seems like it may be struggling under heavier load at idle. The other thing that stands out is the battery dropping from roughly 12.6V after running to around 12.1–12.2V after sitting.

I’m going to check the resting battery voltage one more time tomorrow before touching the car. If the results are similar, I think I’m done with the testing and will take it to a BMW shop for a proper battery load/CCA test, alternator output/ripple test under load, and voltage-drop/ground testing.

[sapote]

. Before starting it today, the battery measured 12.12V. I checked it again and got 12.18V.



Then I turned on the headlights, HVAC blower on high, and rear defroster, with the stereo off. Voltage initially bounced around 13.45V, then dropped to 13.25V, 13.19V, and eventually hovered around 12.72V. The lowest reading I saw was about 12.55V.

With just the rear defroster turned off, voltage came back up to around 13.25V.

You need to fully charge up that batt with a charger overnight before doing the alternator testing with engine running. The badly discharged batt alone placed a heavy load on the alt, and then with additonal accessory load and headlight its output was too low.
a good charged batt should be at least 12.4 to 12.6v engine off.

[Marc E46M3]

Thanks, man! I’ll do that.