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VW Beetle 2012+ Discussion area for the 2012+ Beetle TDI (sometimes call the New New Beetle) based on the PQ35 platform.

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Old February 4th, 2020, 17:16   #1
cannondale0815
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Default Safe to disconnect battery (2014 Beetle TDI)?

Hello group! I drive my 2014 Beetle TDI very infrequently and it often is sitting around for three weeks, sometimes more. Is it ok for me to disconnect the battery during those periods of inactivity (to prevent parasitic drain)? I have done this a few times now and there are no issues with the keyless entry system after, which was my main concern. I do see ECU error warnings on the dash after reconnecting, but those seem to go away by itself once I drive the car (or when I clear with OBDeleven app & dongle). But I also read somewhere that there may be issues with emissions checks when the battery is disconnected, meaning that the car may fail the next DMV emissions check. Is there anything to that?

Thanks!
-J
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Old February 5th, 2020, 15:56   #2
06bluebeetletdi
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The bug will have to be driven 50-100 miles before it will pass state inspection after the battery has been disconnected, otherwise it will not have done all of the checks to set readiness.
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Old February 6th, 2020, 08:32   #3
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Why not just connect a trickle charger if you're concerned about this?
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Old February 6th, 2020, 08:54   #4
cannondale0815
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Originally Posted by 06bluebeetletdi View Post
The bug will have to be driven 50-100 miles before it will pass state inspection after the battery has been disconnected, otherwise it will not have done all of the checks to set readiness.
Thank you -- I suppose there's no way to clear anything using VAGcom or OBDeleven, right? The car has to be physically driven for that distance for the readiness checks?
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Old February 6th, 2020, 08:55   #5
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Why not just connect a trickle charger if you're concerned about this?
It's a good idea but my car is parked in a location where I have no access to a power outlet.
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Old February 6th, 2020, 09:02   #6
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Quote:
Originally Posted by cannondale0815 View Post
Thank you -- I suppose there's no way to clear anything using VAGcom or OBDeleven, right? The car has to be physically driven for that distance for the readiness checks?
Correct. Driven, and run thru a variety of speeds, RPMs, etc.

It's specifically designed so you can't just clear all the codes in the parking lot of the emissions tester.
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Old February 6th, 2020, 09:29   #7
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Correct. Driven, and run thru a variety of speeds, RPMs, etc.
It's specifically designed so you can't just clear all the codes in the parking lot of the emissions tester.
Makes sense -- thank you!
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Old February 7th, 2020, 10:17   #8
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I have cars that sit for a month+ and have no issues. The alarm will go to a low power mode after a while, on the older cars the little LED on the door will stop blinking when this happens, I think the newer ones are the same, but the car should still be fine. No reason to disconnect the battery really.
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Old February 10th, 2020, 05:31   #9
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For whatever reason, our '12 Passat would always kill the battery if it sat for a week. For a while it would kill it after just a few days. Never figured out what the cause was.

I ended up leaving it on a 2a charger if it was going to sit for a while.

-J
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Old February 10th, 2020, 19:18   #10
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Quote:
Originally Posted by oilhammer View Post
I have cars that sit for a month+ and have no issues. The alarm will go to a low power mode after a while, on the older cars the little LED on the door will stop blinking when this happens, I think the newer ones are the same, but the car should still be fine. No reason to disconnect the battery really.
That has always been my experience as well, but with this car, I have seen the battery die after three weeks of inactivity. I attribute it to a combination of bad battery (has since been replaced) and an aftermarket radio with always-on canbus module.

I'll see how this new battery fares and will measure the battery capacity every few days.
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Old February 10th, 2020, 19:52   #11
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If the car can't go into sleep mode due to the aftermarket radio, it will use more power running the battery down faster. That seems to be your issue.
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Old February 18th, 2020, 21:05   #12
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So I have gathered some more evidence related to my parasitic drain.

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 a fuse diagram I found somewhere for my car model, 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)

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.: The aftermarket radio is not the direct source of the parasitic drain -- the drain continues even when the respective fuse is completely pulled, and there is also no measurable voltage drop at that fuse
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Old February 18th, 2020, 21:27   #13
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Not a direct answer to your question, but just wanted mention that your 80 A-hr (80,000 mA-hour) battery can supply that 187 mA drain for months... and months.

Meaning: it's probably not doing any harm, and likely not the main source of any issues you're having.

Could be a symptom of something else I suppose, but I would have thought you'd have found a bigger drain elsewhere.
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Old February 19th, 2020, 04:54   #14
cannondale0815
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Quote:
Originally Posted by Vince Waldon View Post
Not a direct answer to your question, but just wanted mention that your 80 A-hr (80,000 mA-hour) battery can supply that 187 mA drain for months... and months.
Meaning: it's probably not doing any harm, and likely not the main source of any issues you're having.
Could be a symptom of something else I suppose, but I would have thought you'd have found a bigger drain elsewhere.
Thank you Vince -- I've read elsewhere that a 50mA draw is considered normal, so this being more than three times that, I concluded (perhaps incorrectly) that it could be the source of my issue. Perhaps I need to keep looking.

There are a few fuses I didn't check (because I didn't know how to). They are the square looking ones that are in my engine compartment that have a clear plastic cap (pink & green in below photo). I don't know how to access the contacts to do a voltage drop test.

https://photos.app.goo.gl/9gnnLJvxRfTB33sX6

EDIT: I now know those square fuses are called J-Case fuses and the proper way to test them in situ is to pop off the clear plastic lid. I will try to do that in a few days.

Last edited by cannondale0815; February 19th, 2020 at 20:53.
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