2015 Passat parasitic drain

[hgdmartin]

Good morning. Its been a long time since i have visited, and no longer have my '06 Jetta but now own a '15 Passat TDI, and love it. Here is my first real issue after a few years of owning:

A couple months ago i had the battery go dead while wife used the car for quick hops around town; no real lengthy drives. Battery was fairly new so i took to Advance to have them check and charge; no issues noted. I put it back in and drive the car myself for a month or so of long daily commutes. Everything was great. I have not had the time to really investigate for possible issues, and assumed all was good.
Yesterday, daughter cranked up fine after sitting for 3 days, and drove short hop to work. After a few hours of work, she drove home 3 miles with no issues. Parked car for 2 hours, and car wont crank.
I get home last night and battery is reading 11.5V. I jumped it off and allowed it to charge for a while, up to 12.6V. I then mowed yard for 1.5 hours, and volts now at 11.7 after sitting with hood down and all lights confirmed off. I charged back up to 12.6 with electric charger and unplugged cables to set overnight while i sleep on it. This morning, battery still at 12.5V, so i feel good about the battery. Just not sure where to start with looking for this parasitic drain that appears to maybe have gotten much worse than it was a couple months ago.
I do have VAG-COM; is there anything i can look for in error codes or other?
I plan to put together a test lead tonight to begin pulling fuses, but feel quite certain others have had similar issues and can save me a few beginner steps. Any thoughts and suggestions are much appreciated.

I also checked alternator while running, and it is putting out very healthy voltage. Cant remember exact, but somewhere around 13.8 or so.

Thank you in advance,
David in SC

 

[oilhammer]

Search here for the TSB outlining the proper way to check for drains (meaning, you do NOT pull out any fuses).

 

[hgdmartin]

Thanks Oilhammer. I am not having luck with the search. I searched under Our VW Specialist, and get a 404 error code. I then entered parasitic battery drain, tsb, battery, and others in search box and get no matches. Can you please share a little more info? Is it TSB 27-08-04 from year 2008?

Thank you,
David in SC

 

[oilhammer]

Google found it, I just searched "Volkswagen parasitic drain TSB" and here was result #2:

TSB and Matrix for battery drain issues

I'd been having some problems with my 2006.5's battery being dead in the morning when I tried to start my car. I had been using my VagCom to code some things and thought I was all set but the battery dying got worse. I thought I could put an amp meter in line and find the circuit that was...

forums.tdiclub.com

 

[pedroYUL]

Head units are notorious for failing and generating draw that is similar to the way you describe it. Does your radio check out?

 

[hgdmartin]

Well, i let it run a few minutes to get to full charge before shutting it down and locking doors to put her to rest for 2 hours, and then discovered i have no fuse diagram. Not in manual, nor on fuse panel cover. Manual says contact VW.
Scrambling on web right now to see what i can find. Any thoughts are appreciated.
I did IR temperature test while running and only saw one big "644" relay that was about 40 degrees hotter than any others. Once shut down, this one did begin cooling down. Oh boy.

 

[hgdmartin]

Update: After sitting asleep for close to 2 hours, i measured nothing across any of the blade fuses in the engine fusebox. Good thing, i suppose. How does one measure the box square fuses?
I then had to open the door to measure the fuses in the cabin fusebox, which likely woke up the system because i had a wide range of readings on those. Am i missing something here?
I have found fuse diagrams of panels that look similar to mine, but nothing exactly the same. What i have found is from a '14 Jetta, so not the same car. Is there a place to find diagrams for a '15 Passat, or does VW want you to buy them from them?

No voltage loss on the battery overnight. 12.9 last night and this morning. Frustrating. Lost from 12.6 to 11.7 Monday night while i mowed my small yard. Last night, all night and no loss.

These things drive me nuts. I caved and bought a jump box for my daughter to carry with her. Good lesson for her to learn to use.

Any thoughts on tracking down this intermittent drain are appreciated. Thanks All!

David in SC.

 

[oilhammer]

Well first, don't worry about any fuse diagrams or applications.... we can always figure that out later. Try finding any that are carrying a substantial (enough to drain a battery) current first.

You can fool the door by manually latching the door latch with a screwdriver or something, so you can have it open and have access to the dash fuse panel to check those fuses, too.

If it is intermittent, then it could be the radio as stated above, although the NMS uses a different radio supplier than some of the others (I should know, I've had enough of them out to R&R the dashboards in these things).

You could also have a flaky battery. It happens. And many of the testers won't catch them.

 

[pedroYUL]

Yup, if the date in the terminal post of the battery is 14 or 15...I would toss it.

 

[hgdmartin]

Sorry if i have misled. The car is a 2015, but the battery is only a year or so old. I normally grab Interstates, but went with the upper-end one from Advance for this. Recently had a near-new Interstate develop a bad cell in my diesel truck, so all are not perfect.
Advance charged the Passat battery overnite and tested it a month or so ago when first issue came up, and said battery was good. FF to now, and same issue; different day.
Wife tried to start yesterday and it would not crank, so i had her put on charger. I am returning home this eve, and will watch meter tonight as she tried to crank. I am once again leaning toward this maybe being a battery issue.
I had it charged to 12.8V the other day and it would not crank, and volts immediately sunk to about 9, if i remember correct; just with maybe 2-3 turns of the engine. IMO, a battery charged to 12.8V should crank the car. Am i correct?

Thank you for all the advice.
DAvid in SC

 

[oilhammer]

Go to your local dealer and get a new, proper, good battery.

 

[pedroYUL]

This ...battery shouldn't dip below 11v while cranking, any car, any battery

 

[Vince Waldon]

IMO, a battery charged to 12.8V should crank the car.

Not exactly... to crank the car you have to have 12-14 volts but also several hundred amps as well.

For instance, you could string a bunch of AA cells together and get 12V, but only a small fraction of the amps needed.

As batteries age and/or become defective their internal resistance goes up and although they can deliver a normal-looking voltage they are no longer able to deliver enough amperage. Hence the battery load test, which tests both.

 

[oilhammer]

Yep, called a surface charge, and it will not be enough to reliably crank an engine. The rule of thumb is 12.6v nominal (6 cells, 2.1v each), and can drop to 10.5v during cranking. Most ECUs struggle to function below about 9.6v.

If I had a dime for every car that comes in our shop with the same story of "battery tested good, but car won't start" that actually needed a battery, I'd be a very rich man.

Also, while a cold engine is harder to start, hot weather is harder on the battery itself. Which is why most vehicles with batteries mounted outside the super hot environment of an engine compartment typically last longer. In many (most) cases, much, MUCH longer. Around here, it is not uncommon to see VAG products with interior or trunk mounted batteries that last a decade or more under normal use.

 

[hgdmartin]

Thank you all for the very informative discussion. Wife is heading to VW this morning to purchase a battery. I am leaning heavy toward that being my issue now, as i tried to crank last night and it immediately dropped to <9V with less than one turn of engine. Lesson learned; no more Autozone batteries. Not the first time this has happened.
I will reiterate, this happened a couple months ago and Autozone load tested and charged overnite and load tested again and said battery was fine. Would not replace or prorate for a new one. Car has been driven almost every day since with no issues, and now it bites the dust again.

I will report back as soon as new VW battery is in and issue is hopefully resolved.

Thank you all again, and hope all have a wonderful Friday and weekend!
David in SC

 

[eugene89us]

@hgdmartin and @oilhammer You all hit the nail on the head. My 2014 has gone through the second battery replacement (on its third overall counting one car came with). For some reason, Passat battery only lasts about 3 to 4 years, at least in my case. I was so upset that I lost my last battery receipt, since I believe the battery has a 5-year prorated warranty after full replacement of 3 years. But anyways, the first time battery died was when Passat was my primary car. One morning before work, it would not crank. I borrowed wife's car and went to work. Then a family member bought me another one.

Second time, my mom was the primary driver. She actually mentioned to me that a couple times, the car took many more cranks to start. Says restarting is fine, but initial start after car sits is slow and sluggish. We took the car to AutoZone, since I figured it was the battery. But once you drive it and that powerful alternator recharges it, the battery came back okay. I warned her that the time of no start will come, I could just feel it. Sure enough, a couple days later, I get a call that her car did not start. Exchanged the battery and all is well again.

So the moral of the story, these batteries are weird since they will pass the load test with flying colors, yet won't start a car after it sits overnight. And what is especially strange is how short Passat's battery lifetime is! My 2018 diesel Bimmer is still going strong on original H9-equivalent Varta battery. But Bimmer battery lives in the trunk, in the cool space away from engine heat. Though Passat's battery is covered in protective sheath, I feel the "surface of the sun" conditions certainly lead to its deterioration. I spend a lot of free time on BimmerPost, where many of BMW owners ask whether their 7 or 8 year old battery needs replacement (when weird electrical codes start to pop up). I just wish Passat could at least go 5 years, but at least dealer battery is not much more expensive than AutoZone or Advance batteries (though latter always has excellent coupons).

Last Passat battery was made by Varta (replaced in 2021), in my opinion one of the best manufacturers. Though there is not much competition in the battery market, despite the variety of name brands out there. Good luck, please keep us posted!

 

[hgdmartin]

Well, I am calling this episode over; VW dealership battery installed Friday morning and all codes have now cleared and things appear to be back to normal. Thank Gosh. Hard on an old man to keep 4 cars, 2 boats, 3 lawn mowers, and assorted other junk going, along with a job and family. Don't need my trusty VW playing mind games. Next time, i will know to not buy Advance batteries.

Thank you so much for everyone's help. Hope you all had a nice weekend.
David in SC

 

[Boost&BlueGrass]

Curious if you had any problems after the new battery? Just had this same exact problem on my 2015 Passat TDI. Went through the entire car and found the radio was the culprit drawing power when the car was off. Pulled the fuse and haven’t had a problem since then.

 

[Jetta_Pilot]

I too have a 2015 Passat and have never found a fuse diagram anywhere and the dealer will not pass the info on.

So my workarouind is this, a bit expensive though. Buy the Littlr fuse smart glo fuses and swap the old fuses out to these. If anything blows, the Little Fuse Glo fuses will glow telling you which has blown. You can buy them in kits of about 30 fuses both sizes.

 

[06bluebeetletdi]

Bit of interesting info: i have a 2013 beetle, ended up with a parasitic draw after installing the vw fog light retrofit kit, a friend who is a vw tech looked at all the fuse diagrams for beetles and never found one that matched my car. Finally found out one of the fuses was waking up a module every hour or so. Moved the wire from the fog light harness to an empty fuse slot and installed a new fuse, problem solved, no more draw. So there may not be an accurate diagram for the car, I’ve never had a reason to ask him to check for the passat.