Issue with Electrics / Battery in 2013 VW Passat

MinxOfInsolence · 04-02-2025 12:48PM #1

Hi all,

I have a 131 Volkswagen Passat that has a particular issue that even regular mechanics can't identify. They have recommended I go to an Auto Mechanic and doing some research, it seems like they are expensive as hell and bill by the hour!

So I wanted to see if anyone might have some insight here before throwing money into that.

Make and Model: 131 Volkswagen Passat Highline 2.0 Diesel

Issue: Battery drains when car is not even running. A simple jump start will fix the issue as long as the car is driven for around 20 minutes afterwards. But the car needs to be driven every day, otherwise another jump start is needed. If I have driven it all week, I can not drive on Saturday and it will still work on Sunday. But if i were to leave the whole weekend without driving, the car will not start on Monday morning. Something electrical is draining the battery whenever it is not running.

A few things I thought of and checked up to now.

- the auto start being on. this is not an issue though as it is not in operation when the car is turned off.

- light switch being set to auto, rather than off. Tested a few times and it does not make a difference

- air con being left on - doesn't seem to make a difference.

One thing that I can't check but am suspicious of is there is a custom stereo system in the car that I believe is not the standard that comes with this model. Happy to provide pictures of this if needed.

Is there anything else I can check to see if it might be the source of the issue? Has anyone come across this issue in the same model and year?

Any and all help is appreciated here as it is driving me crazy and making me think it would be better to sell it and move to something less troublesome, but that't not cheap in the current market.

CMOTDibbler · 04-02-2025 01:33PM

You clearly have a parasitic drain on the battery and number one cause of that is an aftermarket fitment like a stereo. Easy way to check if it's that (or some other unit) is to find and pull the fuse for that item.

This may pull power from other functions, so make sure it doesn't affect some basic functionality like lights or indicators etc.

A more definitive method would be to (with the car and all lights etc. off) measure the current draw at the battery. It should be very low (about 0.05 amps), if not, start pulling fuses one by one. The one which drops the current draw is the culprit.

mondeoman72 · 04-02-2025 01:38PM

As a stop gap, you could disconnect the battery when parked up, although this may reset the radio, and various settings.

User1998 · 04-02-2025 01:41PM

Can you post a photo of the radio? I’ve had the same issue with certain radios if they aren’t installed correctly.

What about the battery itself tho? When was it last replaced?

ongarite · 04-02-2025 02:55PM

As above, if you want to save big money on resolving issue, borrow or buy multimeter & do the troubleshooting yourself.

Measure & observe current draw on battery & pull each fuse & see does current drawn fall. Then isolate all devices on that fuse line.

Aftermarket radio is very likely to be the cause

kirving · 04-02-2025 06:23PM

It's almost certainly the aftermarket radio, or how it was installed.

While you could pull the "radio" fuse(s), the same fuse(s) might also be feeding something else, or the radio could be using another source.

I'd recommend pulling out the radio temporarily, and at minimum making sure that it's only pulling power from the original radio plug and hasn't been wired in somewhere else entirely.

mk7r · 04-02-2025 06:51PM

The Passat used a canbus radio so it has a canbus signal to turn the radio on and off, the cheaper aftermarket radios don't support this so it's very likely your cause

User1998 · 05-02-2025 02:34AM

https://www.boards.ie/discussion/comment/123134573#Comment_123134573

The common aftermarket CarPlay radios do come with a canbus adapter but sometimes they aren’t installed correctly. I’ve replaced 20+ VW’s with aftermarket units with no issues but have seen one or two that I didn’t install myself drain the battery. If you look closely at the power button it may still be lighting up even after the car is switched off

MinxOfInsolence · 05-02-2025 12:21PM

So embarassingly, it seems that my research into the stereo was not correct and the one in my car is the standard for the Highline model. So it now seems unlikely that the stereo is the cause.

I think my best bet like others have said is to get a multimeter and figure out whats causing the drain.

16-02-2025 12:28PM

Try getting your battery checked as well.

A bad battery will give similar symptoms .

A simple check is to disconnect the battery for the few days .

This would prove parasitic drain or bad battery

Issue with Electrics / Battery in 2013 VW Passat

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