Parasitic drain

[devanduzen]

Hello all first post.

This is my first bmw and i love it his name is gunter. He seems to have a very slow drain when left sitting for a couple of days. He did have an aftermarket security system but it was removed. Battery is brand new and tests in spec and alt is doing its job. It does show that the trunk is open on the dash. Its not. Have checked the cabin lights they shut off. Not sure where else to look. Any advice would be greatly appreciated.

Many thanks.

David

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[MarcoZandrini]

I’m wondering if the indication that the trunk is open means the trunk light is on.

There are several good parasitic current drain videos on YouTube. Basically, you connect a digital multimeter in series with the ground cable at the battery to measure the current drain. Then you start pulling fuses until you find the bad circuit.

[shadowpuck]

i think an e39 would be new enough that i'd want to measure voltage across fuses with the car asleep as that method won't accidentally wake up a module, bus, etc.....

[devanduzen]

I’m wondering if the indication that the trunk is open means the trunk light is on.

There are several good parasitic current drain videos on YouTube. Basically, you connect a digital multimeter in series with the ground cable at the battery to measure the current drain. Then you start pulling fuses until you find the bad circuit.

Thanks for the reply. I temp fixed it by pulling the fuse for interior/trunk lights. Has been fine since. Weird thing is there is no light in the trunk. Now just have to figure out which light is culprit.

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[MarcoZandrini]

It sounds like the trunk light is the culprit.

[bmwdirtracer]

I would think that the trunk latch is the culprit.Because the central locking believes the trunk is open, the car isn't going to go to sleep.

With key on, so that you can see the "open trunk" indicator, try pushing down hard on the trunk lid, see if the light goes out.

You can also try using a screwdriver to latch the trunk latch while the trunk lid is open.

If the light still doesn't go off, the General Module needs to be interrogated with a good diagnostic computer.

[shadowpuck]

hi chris!

[MarcoZandrini]

Welcome back, Chris!

[devanduzen]

I would think that the trunk latch is the culprit.Because the central locking believes the trunk is open, the car isn't going to go to sleep.

With key on, so that you can see the "open trunk" indicator, try pushing down hard on the trunk lid, see if the light goes out.

You can also try using a screwdriver to latch the trunk latch while the trunk lid is open.

If the light still doesn't go off, the General Module needs to be interrogated with a good diagnostic computer.

Hey. Thanks yes we tried that it still stays on. Its been on since my buddy got the car. I assume thats why when i pulled the number 4 fuse the issue stopped allowing the car to sleep. I am new to bmw world what is this sleep term i keep reading. Sorry if dumb question

Thanks

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[shadowpuck]

all cars have a process for going to "sleep" - that's not a BMW thing necessarily.
basically, once the car goes to sleep its at its lowest power usage point of time where most of the power consumers have shut off.

i'll reiterate my suggestion from earlier for chasing down parasitic drain:
i would check for any activity across each fuse after the car has gone to sleep. if you search google you'll find several good articles on this - as i recall, it's around 17 minutes or so once all doors are closed, all lights off, etc. the car should go into a power down mode - or, sleep, as we call it. once that happens, you can begin checking each fuse for activity (this is done by simply putting a meter across the fuse and noting the reading). if you find anything beyond a very small trace of activity, that's a suspect to be investigated.

here's two good articles from the makers of the autologic scan tool, i found these by typing e39 parasitic drain in google:
https://us.autologic.com/news/mini-b...specifications

https://us.autologic.com/news/testin...e-voltage-drop

if you go to youtube and search for humble mechanic and parasitic drain he has a great video on this as well. it's for volkswagen but the concepts are identical.

the later cars (e60, etc.) have some pretty good built in diagnostics for drain issues, but, i think the e39 was too early for that....

[devanduzen]

all cars have a process for going to "sleep" - that's not a BMW thing necessarily.
basically, once the car goes to sleep its at its lowest power usage point of time where most of the power consumers have shut off.

i'll reiterate my suggestion from earlier for chasing down parasitic drain:
i would check for any activity across each fuse after the car has gone to sleep. if you search google you'll find several good articles on this - as i recall, it's around 17 minutes or so once all doors are closed, all lights off, etc. the car should go into a power down mode - or, sleep, as we call it. once that happens, you can begin checking each fuse for activity (this is done by simply putting a meter across the fuse and noting the reading). if you find anything beyond a very small trace of activity, that's a suspect to be investigated.

here's two good articles from the makers of the autologic scan tool, i found these by typing e39 parasitic drain in google:
https://us.autologic.com/news/mini-b...specifications

https://us.autologic.com/news/testin...e-voltage-drop

if you go to youtube and search for humble mechanic and parasitic drain he has a great video on this as well. it's for volkswagen but the concepts are identical.

the later cars (e60, etc.) have some pretty good built in diagnostics for drain issues, but, i think the e39 was too early for that....

Thanks i will try it that way. Does anyone know where the sensor is in the trunk latch? Thanks. I did pull the fuse for interior lights was fine for a month. Then didnt drive for couple of days and got the slight flicker when it started wasnt dead but something is still very slowly draining it.

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[MarcoZandrini]

You have to remember that a lead acid battery is permanently damaged when it's discharged below a specific charge level. Basically, the chemistry changes and it damages the lead plates, decreasing their capacity. Your battery may be toast.

shadowpuck, checking across a fuse will always show zero volts. Don't you mean to pull the fuse and then check for current across the fuse holder contacts?

[shadowpuck]

You have to remember that a lead acid battery is permanently damaged when it's discharged below a specific charge level. Basically, the chemistry changes and it damages the lead plates, decreasing their capacity. Your battery may be toast.

shadowpuck, checking across a fuse will always show zero volts. Don't you mean to pull the fuse and then check for current across the fuse holder contacts?

hey marco - nope - check here (https://us.autologic.com/news/mini-b...specifications) and see this (https://us.autologic.com/news/testin...e-voltage-drop) voltage drop across a fuse. allows checking without pulling the fuse - on many recent vehicles disrupting the circuit can cause things to power down, power up, etc.

you are reading drop (usually in milliamps)....

[devanduzen]

You have to remember that a lead acid battery is permanently damaged when it's discharged below a specific charge level. Basically, the chemistry changes and it damages the lead plates, decreasing their capacity. Your battery may be toast.

shadowpuck, checking across a fuse will always show zero volts. Don't you mean to pull the fuse and then check for current across the fuse holder contacts?

I thought that at first but the battery tests fine. Its still warranty covered its only 6 months old big sucker.

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[devanduzen]

I thought that at first but the battery tests fine. Its still warranty covered its only 6 months old big sucker.

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Ok quick update. Went to batt place i deal with. The did tests. Here are results.

Voltage asleep 12.16.
Measured 595 cca
Rating 900 cca

Very low.

Alt running 14.1

Also has 100 milliamp draw when car is off

Got a good cytech charger with agm setting and threw it on. I still suspect its the trunk. The latch handle is totally shot so thats why it thinks the trunk is open. Going to open up trunk hatch and disconn latch handle wiring see if. That clears it. Thanks for all the ideas.

David

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[MarcoZandrini]

That 100ma draw is too high. The cca test shows that the battery is either not fully charged or it’s damaged.

[MIKYZZ4]

Draw should be less than 50ma.

[shadowpuck]

yeah, the spec i've often found for an e39 is 40ma after 16 minutes. but, regardless, agreed totally - 100ma (if the car is truly asleep) is too much.

[MarcoZandrini]

Put an ****** tablet in the tank! /s

[devanduzen]

Put an ****** tablet in the tank! /s

Hu?

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[MarcoZandrini]

The website put the “*****” in place if a well known prescription sleep aid the begins with “A” and ends with “N”!

[devanduzen]

Lol. Plastic explosive more like it. Now have transmission issue i hate this car

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