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Discussion Starter · #1 · (Edited)
I've been having parasitic drain in my 2014 VW Beetle TDI. Even when parked, the battery voltage slowly decreases -- perhaps about .2 volts per day (measured with a digital multimeter), give or take.

Through voltage-drop measurements across all fuses, I found that one particular 20 amp fuse (no. 23 in the interior fuse panel) is having a voltage drop of .6 mV between the two contact points, which, according to this voltage drop chart, translates into 187 milliAmps.

The test was performed with all door latches in the locked position, then waiting a couple of hours to ensure all systems enter sleep mode.

According to this diagram, the fuse in question (fuse no. 23 in interior panel) serves the following purposes:

Rain/light recognition sensor -G397-
Vehicle Electrical System Control Module -J519-
Telephone Transceiver -R36-
16-pin connector -T16-, data link connector -GX22-

I checked my car for error codes using OBDeleven, and found the following faults that may be related:
- Gateway module: Telephone Transceiver (No signal/communication)
- Telephone module: Telephone microphone (open circuit); Left audio channel for speech/telephone (open circuit); Right audio channel for speech/telephone (open circuit)

Now, I want to mention that I am using an aftermarket Android radio (see my signature) and these errors have been there for a while and keep coming back periodically when cleared. My mobile phone is connected via BT directly with the Android HU, so I don't need the car's telephone function anymore. But I wonder if the above Telephone related errors could be the cause of the parasitic drain somehow. Are there perhaps some coding changes I can perform to tell the car that I don't need it's Telephone function and also not the speech control stuff?

Any suggestions appreciated!

P.S.: Neither my aftermarket radio nor the aftermarket rear view camera are the direct source of the parasitic drain -- the drain continues even when the respective fuses are completely pulled, and there is also no measurable voltage drop at those fuses
 

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First off, props on the diagnostic process. :thumbup:
I've found that it's hard to sell people on the voltage-drop method of diagnosing a draw - but, it does work. And, it's a lot less invasive (read: faster and more accurate) than the 'yank the fuses until the draw is gone!'

I'll assume that homework is done correctly, and that fuse 23 does, in fact, provide power to those four things (and nothing else.)
Seasoned master tech (me, not VW - another German brand) says:
This is the point where you unplug control units. Typically, I go in order of 'fastest to access, to longest to access' (because, best use of time in the shop.) But, that's also weighted by 'importance in the vehicle.'
What that means: unplug the quickest-to-get-to thing(s) first, UNLESS said unplugging is likely to cause a vehicle-wide freakout.
Phone module: low/no impact.
Rain/Light sensor: low/no impact.
OBD connector: well, it can't cause a draw (but, no 'insurance dongle' plugged in there, right?)
The J519 module: controls a lot. He gets unplugged last. Plus, I'm not certain as to what all actually goes thru that box - so, being a 'important control unit', there's the possibility of a 'thing connected to it' actually being the cause of the draw (read: not the control unit itself.)

I hope all of that makes sense?
 

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Discussion Starter · #3 ·
First off, props on the diagnostic process. :thumbup:
I've found that it's hard to sell people on the voltage-drop method of diagnosing a draw - but, it does work. And, it's a lot less invasive (read: faster and more accurate) than the 'yank the fuses until the draw is gone!'
Thank you cuppie for those suggestions. Am I even right in assuming that 187mA is too much draw, or could that be considered normal?
 

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Oh, 187mA (after the vehicle goes to sleep) is way too high. Normal rest-state power consumption of a car is in the 5-50mA range (depending on the particular car.)
187mA will kill a battery dead in just a couple of days (assuming 100% charged & heathy battery.)
 

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First off, props on the diagnostic process. :thumbup: I've found that it's hard to sell people on the voltage-drop method of diagnosing a draw - but, it does work. And, it's a lot less invasive (read: faster and more accurate) than the 'yank the fuses until the draw is gone!'
It's true, even the so called pro's pull fuses. It's absolutely stupid to do that with today's cars. Every time you pull a fuse, you have to wait till the car goes to sleep again.
 

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Discussion Starter · #6 ·
Oh, 187mA (after the vehicle goes to sleep) is way too high. Normal rest-state power consumption of a car is in the 5-50mA range (depending on the particular car.)
187mA will kill a battery dead in just a couple of days (assuming 100% charged & heathy battery.)
Thank you cuppie! This car is still under certified warranty so I'll likely just bring it to a VW dealership and have them troubleshoot further. At least I feel I sufficiently narrowed it down. Hopefully they will employ a similarly scientific method to take this further.

Sent from my Pixel 3 using Tapatalk
 

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Discussion Starter · #7 ·
Hello fellow enthusiasts, several months have passed since my original post at the top, and the world truly is a different place now.

Anyway, I haven't brought the car to the dealer yet, but have been doing a lot more testing. I have to conclude that my original finding of one single fuse having a parasitic draw may have been incorrect. I repeated the test a few more times (latching & locking car doors, waiting a couple of hours, then perform voltage drop test on all fuses in driver compartment and engine bay), and I now don't have a single fuse that shows any drop on my multimeter. I guess during my initial tests I didn't wait long enough for the car to truly have gone to "sleep".

I even tested all cartridge fuses in the engine compartment. Those were a bit tricky to pop the plastic lid off. But I managed to do that and none of them show any draw.

So now I'm in a situation where the battery still slowly runs down over the course of a few days, even though none of the fuses show a voltage drop. But when I test several times a day I can see that the battery still looses about .2 volts (give or take) over the course of a day.

What else could be the culprit? There must be something else depleting the battery that is not behind any of the normal fuse circuits.

Any advice is greatly appreciated!

@cuppie, perhaps you have another suggestion? :)
 

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@cuppie, perhaps you have another suggestion? :)
Yes - actually confirm that it has a draw. Need a clamp-on ammeter that can read low mA DC.

I’d hate to ask the obvious. But....

What’s the health of the battery? Will it Pass a load test?
This, too. A bum battery will do the same thing that you're seeing.
 

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Discussion Starter · #10 ·
Yes - actually confirm that it has a draw. Need a clamp-on ammeter that can read low mA DC.

This, too. A bum battery will do the same thing that you're seeing.
I confirmed with an amp clamp that there is a draw of ~200 milliamps when the car is asleep. I measured that by clamping around the two positive cables that originate from the positive battery post.

The battery is in good health and only three months old, as I had to replace it again during COVID-19. I now disconnect it every night to ensure it stays healthy. And I measure if daily to ensure it never drops into the danger zone.

Also, I did an AC test across the positive and negative battery posts while the engine is running. I get a reading of around 0.020 V (AC). So I suspect this may mean an alternator diode issue?

The car is going to the shop today and I am having the dealer take a closer look.
 

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20mVAC actually isn't horribly bad - generally, up to 50-100mVAC is acceptable (depending on the car.) The definitive test is with an oscilloscope, so you can see the output waveform.

First, though, check that your DVOM truly blocks DC voltage in the AC ranges (not all do): Set the meter to 20VAC (or closest equivalent), and measure battery voltage (engine NOT running.) Make sure that the meter reads 0.00VAC there.

Because you have that clamp-on ammeter, use it to check the alternator itself for a draw! Just hang it on the alternator output wire - see anything?
 

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Discussion Starter · #12 ·
20mVAC actually isn't horribly bad - generally, up to 50-100mVAC is acceptable (depending on the car.) The definitive test is with an oscilloscope, so you can see the output waveform.

First, though, check that your DVOM truly blocks DC voltage in the AC ranges (not all do): Set the meter to 20VAC (or closest equivalent), and measure battery voltage (engine NOT running.) Make sure that the meter reads 0.00VAC there.

Because you have that clamp-on ammeter, use it to check the alternator itself for a draw! Just hang it on the alternator output wire - see anything?
Thanks man -- the car is with the dealer right now. I gave them a detailed break-down of everything I have tested and found. I hope they will know what to do next. Once I get the car back (they already told me it may take a couple of weeks), depending on their findings, I'll conduct the alternator test next.

Thanks for all your help so far!
 
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