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Discussion Starter · #1 ·
Hi there, sadly I didn't find any help from old topics.

After not driving my car for a month due to being sick from covid, my battery was dead. I though that's normal, bearing in mind it's cold here (about 0C). Got a jump start, drove for about two hours and didn't have any problems for the next week. After two weeks of driving normally, I parked my car and didn't drive it for exactly a week, after which it couldn't start it again. Got the car to my mechanic and he checked for drains and saw that fuse 41 is draining about 0.09A. I plugged my radio out, and it dropped to about 0.06-0.07A. It's an aftermarket Panasonic radio, haven't had problems with it for years. With the amp removed, it draws 0.01A. It's the standard amplifier (non HK). I'm using a Varta 77Ah battery, it's 2 years old and still in warranty.
The car is E46 330xi pre-facelift.

Is this a normal power draw from the amp? Could it be a bad battery? What else could be my problem and how should I diagnose it?

Thanks in advance!
 

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2004 330Ci 115k miles
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Battery probably never got fully charged after it died. Charge it on 10A (or higher) for at least 8 hours.

Also, if the battery went dead 2-3 times or more, it won't hold much charge. Car batteries are never supposed to get fully discharged.
 

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Discussion Starter · #4 ·
I was with my mechanic and was watching the multimeter at all times. I'll try waiting for 16 minutes next time and see what happens!
 

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E30M3 Race F10 535 R1150Rt M Coupe
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That's the key, wait for 16-18 minutes, then see if the drain is still there?
 

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That’s 90ma. That’s high but not that high. It seems the culprit is the factory amp. Check the voltage on the cream colored wire at the amp. That wire carries the 12VDC “turn on” signal from the head unit. The head unit may be sending this signal even when it’s off. Btw, the head unit gets power as long as the battery is connected. This is used to maintain the radio presets.
 

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Sounds like you're doing the right thing with your testing, but I'd encourage you to use a multimeter than reads down to microamps (0.001A) rather than just milliamps (0.01A). Not because you need to know in millamaps but because they have an accuracy of +/- a given number of "counts", that is +/- a given number of the least accurate digit. Typically, it can be +/- 3 counts. So a reading of 0.09A could actually be 0.12A or 0.06A, and the meter would be in spec. With a multimeter that read it as 0.090A, that would be 0.093A to 0.087A, allowing you to trust that the milliamp value is correct to the nearest digit.

Though I also agree with BaliDawg, it's possible the car's fine and the battery didn't get a full charge after being run down. Or, if it did, it's not the first time it's been run down and the plates have sulphated. But you're definitely doing the right thing to test the drain before spending on a new one!
 

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Just to confirm, you're closing the trunk ( I close teh lid on the wires and leave the meter outside) and waiting 15 - 20 minutes? Why not just pull fuses instead of the whole radio? Has this been going on since you changed radio unit?
I seem too recall amp being source in the past.
 

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Discussion Starter · #10 ·
Just to confirm, you're closing the trunk ( I close teh lid on the wires and leave the meter outside) and waiting 15 - 20 minutes? Why not just pull fuses instead of the whole radio? Has this been going on since you changed radio unit?
I seem too recall amp being source in the past.
Well, I'm not closing the trunk, I'm clicking the lock on it though, so that's basically the same as closing it I guess. The lights don't work inside the trunk when the lock is clicked. With the fuse pulled out it doesn't drain. I pulled out the whole radio in order to see if the problem is from that or not.

That’s 90ma. That’s high but not that high. It seems the culprit is the factory amp. Check the voltage on the cream colored wire at the amp. That wire carries the 12VDC “turn on” signal from the head unit. The head unit may be sending this signal even when it’s off. Btw, the head unit gets power as long as the battery is connected. This is used to maintain the radio presets.
As I said, I've removed the head unit and without it the amp drained about 0.06 - 0.07. I thought that it wouldn't get power if there's no head unit. Do you happen to have a picture of the wire that I need to check? I'm currently not near the car and I can't find a cream colored wire on pictures from google. Thanks!


Sounds like you're doing the right thing with your testing, but I'd encourage you to use a multimeter than reads down to microamps (0.001A) rather than just milliamps (0.01A). Not because you need to know in millamaps but because they have an accuracy of +/- a given number of "counts", that is +/- a given number of the least accurate digit. Typically, it can be +/- 3 counts. So a reading of 0.09A could actually be 0.12A or 0.06A, and the meter would be in spec. With a multimeter that read it as 0.090A, that would be 0.093A to 0.087A, allowing you to trust that the milliamp value is correct to the nearest digit.

Though I also agree with BaliDawg, it's possible the car's fine and the battery didn't get a full charge after being run down. Or, if it did, it's not the first time it's been run down and the plates have sulphated. But you're definitely doing the right thing to test the drain before spending on a new one!
Sadly with my current state I can't afford a new battery for the next month at least (just bought a house today!), and spending money on a new battery when that might not be the problem won't fix anything. I don't have a multimeter with microamps, I'll try to find one and check it again. I haven't had a full battery drain, I still had juice to unlock the car and light up the dash, but not enough to start. I can't remember the reading on my BC the last time I couldn't start, but I think it was about 11V.
 

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I've not tried the latch close. But I've read others do. Sounds like next step is to disconnect amp. As I said, that has been discussed on here before, I believe. Can you not just pull the plug on it?
 

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Discussion Starter · #12 ·
I've not tried the latch close. But I've read others do. Sounds like next step is to disconnect amp. As I said, that has been discussed on here before, I believe. Can you not just pull the plug on it?
Yes, I've plugged out the amp and the head unit, and it dropped to 0.01A. Should I be checking something else or is it 100% the amp?
 

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If memory serves, about 0.04 is normal upper limit. So 0.01 is quite low. It would seem your amp is the culprit. Perhaps try driving for a few days with it disconnected.
 

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Discussion Starter · #16 ·
If memory serves, about 0.04 is normal upper limit. So 0.01 is quite low. It would seem your amp is the culprit. Perhaps try driving for a few days with it disconnected.
The car was out for 5 days with amp unplugged and had no problem starting it on the 6th day. I guess that I'll have to get a new amp and see what happens. Do you know if I can buy a used amp and just plug it in or does it need coding?
 
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