Dash resetting while driving/electrical issues

chillywings · 04-30-2021, 10:54 PM

Hi guys,

So I've had a strange issue crop that I'm trying to chase down. I was driving once 2-3 weeks ago and the the entire dash, idrive and everything briefly shut down and came back on. Engine didn't lose power. The idrive had a big red warning saying electrical issues don't drive. Then this weekend I was driving down the highway and the same thing happened. Cruise control cut out but I didn't lose engine power. Then I turned the cruise control back on and it happened again. And again. So I gave up on cruise control but within a few minutes it happened again and kept going to the point where it was just happening repeatedly. I tried the check control function and a TPMS error was coming up on several of the resets. Turned around to go home and of course it chilled out. It's happened intermittently since and seems to start happening after doing modest to hard accelerations. It has no trouble starting, but in later iterations the radio will go out as well and once I was trying to put up the top (E93) after this happened and power seemed to be intermittent.

I went to the autoparts store to have them check my battery and alternator.. when the tested the battery directly at the terminals it was fine but when they used the terminals under the hood it said bad cell (though I think he may have had a poor ground for that). When I started the car the tester said bad diode. So I went home and got out the multimeter and when the car is running it reads 0.5V of AC current at the battery posts under the hood. However when I disconnect the output wire from the alternator and do a diode test between the casing and output terminal, it reads 0.445V in one direction and 0 in the other. Which would make me think the diodes are okay. I found an in depth article on alternator diode testing that said all alternators leak some AC. So my question is.. is 0.5V AC too much or is that normal for our alternators? Car is a 2011 335is (N54, LCI).

Another thing to note here is that, with the car off, I read 11.8V from the OBD port. This initially made me think it might be the battery. When I measured from the battery terminals, it read 12.1V and when I disconnected the terminals it read 12.5V. Is that much of a voltage drop expected when connecting the terminals? Battery is ~2.5 years old.

Also, when I scanned for codes after this there were a bazillion. I cleared them and only the TPMS code (A3C3) stayed. I found another post with similar issues suggesting that replacing the TPMS module fixed the issue (with others reporting the voltage regulator being the culprit). At one point I hooked up the OBD reader while driving the car and it read a steady 13.8V. However the electrical freakout didn't happen during this time. Also, again when measuring from the terminals with the multimeter the reading is higher. 14.6V with the car at idle. https://www.e90post.com/forums/showthread.php?t=1246164

Seems to me like there's a good chance the TPMS module going bad would be a symptom of something else... eg the alternator diodes going bad. Or could it be that the battery is on the edge? Or perhaps the battery just isn't charging well bc of the alternator? Does anyone know if the voltage regulator also happens to contain the diodes? Could I replace that instead of the whole alternator?

Sorry for the novel.

ctuna · 05-01-2021, 12:51 AM

Your battery is suspect try putting a full charge on it ans see what it
measures . If when fully charged it drops overnight you probably have a
bad battery. There was a recall for the power wire connection leading
into the cabin fuse box for some years.
Other problems that can cause voltage drops are water in the battery compartment
causing corroded connections or bad ground straps connecting from
the Engine to chassis.
Battery voltage on a new one is 12.6 when it gets below 12.4 it's not good.
12 volts is very low.
When you put in the last battery where you careful to get the same type and register it
or reprogram the car for the Size and Type.
You cannot go from Lead Acid to AGM without reprogramming or vice a versa.
13.8 does not indicate a bad Alternator Voltage.
The car has the capability to alter the output dependent on conditions.

https://www.e90post.com/forums/showthread.php?t=1496247

chillywings · 05-01-2021, 01:09 PM

Thanks for the tips. I activated the hidden menu while driving today and it seems like over voltage isn't the issue. I'll pay closer attention to the battery. Also iirc my ground strap wasn't in the best shape so I'll check on that too.

However the 0.5V AC still worries me. Hoping someone knows something about that.

04-30-2021, 10:54 PM	#1
chillywings New Member 2 Rep 16 Posts Drives: BMW 335is Join Date: Jul 2020 Location: MA iTrader: (0)	Dash resetting while driving/electrical issues Hi guys, So I've had a strange issue crop that I'm trying to chase down. I was driving once 2-3 weeks ago and the the entire dash, idrive and everything briefly shut down and came back on. Engine didn't lose power. The idrive had a big red warning saying electrical issues don't drive. Then this weekend I was driving down the highway and the same thing happened. Cruise control cut out but I didn't lose engine power. Then I turned the cruise control back on and it happened again. And again. So I gave up on cruise control but within a few minutes it happened again and kept going to the point where it was just happening repeatedly. I tried the check control function and a TPMS error was coming up on several of the resets. Turned around to go home and of course it chilled out. It's happened intermittently since and seems to start happening after doing modest to hard accelerations. It has no trouble starting, but in later iterations the radio will go out as well and once I was trying to put up the top (E93) after this happened and power seemed to be intermittent. I went to the autoparts store to have them check my battery and alternator.. when the tested the battery directly at the terminals it was fine but when they used the terminals under the hood it said bad cell (though I think he may have had a poor ground for that). When I started the car the tester said bad diode. So I went home and got out the multimeter and when the car is running it reads 0.5V of AC current at the battery posts under the hood. However when I disconnect the output wire from the alternator and do a diode test between the casing and output terminal, it reads 0.445V in one direction and 0 in the other. Which would make me think the diodes are okay. I found an in depth article on alternator diode testing that said all alternators leak some AC. So my question is.. is 0.5V AC too much or is that normal for our alternators? Car is a 2011 335is (N54, LCI). Another thing to note here is that, with the car off, I read 11.8V from the OBD port. This initially made me think it might be the battery. When I measured from the battery terminals, it read 12.1V and when I disconnected the terminals it read 12.5V. Is that much of a voltage drop expected when connecting the terminals? Battery is ~2.5 years old. Also, when I scanned for codes after this there were a bazillion. I cleared them and only the TPMS code (A3C3) stayed. I found another post with similar issues suggesting that replacing the TPMS module fixed the issue (with others reporting the voltage regulator being the culprit). At one point I hooked up the OBD reader while driving the car and it read a steady 13.8V. However the electrical freakout didn't happen during this time. Also, again when measuring from the terminals with the multimeter the reading is higher. 14.6V with the car at idle. https://www.e90post.com/forums/showthread.php?t=1246164 Seems to me like there's a good chance the TPMS module going bad would be a symptom of something else... eg the alternator diodes going bad. Or could it be that the battery is on the edge? Or perhaps the battery just isn't charging well bc of the alternator? Does anyone know if the voltage regulator also happens to contain the diodes? Could I replace that instead of the whole alternator? Sorry for the novel.
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05-01-2021, 12:51 AM	#2
ctuna Lieutenant General 1918 Rep 13,117 Posts Drives: 325xi 06 wagon MT Join Date: Jan 2010 Location: Santa Cruz, Ca iTrader: (0)	Your battery is suspect try putting a full charge on it ans see what it measures . If when fully charged it drops overnight you probably have a bad battery. There was a recall for the power wire connection leading into the cabin fuse box for some years. Other problems that can cause voltage drops are water in the battery compartment causing corroded connections or bad ground straps connecting from the Engine to chassis. Battery voltage on a new one is 12.6 when it gets below 12.4 it's not good. 12 volts is very low. When you put in the last battery where you careful to get the same type and register it or reprogram the car for the Size and Type. You cannot go from Lead Acid to AGM without reprogramming or vice a versa. 13.8 does not indicate a bad Alternator Voltage. The car has the capability to alter the output dependent on conditions. https://www.e90post.com/forums/showthread.php?t=1496247 Last edited by ctuna; 05-01-2021 at 01:21 AM..
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05-01-2021, 01:09 PM	#3
chillywings New Member 2 Rep 16 Posts Drives: BMW 335is Join Date: Jul 2020 Location: MA iTrader: (0)	Thanks for the tips. I activated the hidden menu while driving today and it seems like over voltage isn't the issue. I'll pay closer attention to the battery. Also iirc my ground strap wasn't in the best shape so I'll check on that too. However the 0.5V AC still worries me. Hoping someone knows something about that.
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