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Noob 2008 Passat Owner....well, it's my kids car at college. I am well-versed in working on cars, American Late-Model cars lol, but this one is puzzling me since I can't find any parts diagrams for the Passat.

Daughter came to her car a few times in the last week to discover that the battery was dead. So, I do own a vagcom and it said that the battery is great, as well as the charging system.

Went through the obvious questions....
- Did you leave the interior light on?
- Did you leave the headlamps on....next thing I am buying her is the auto headlamp upgrade from ebay.

Then my kid said that because it was a whopping 50 degrees, she used the heated seats and heated mirrors....brrrrrrrrrrr.

So, my wife brought the car home for the weekend and took the car to my kids hockey practice where again....the battery died. Used the heated seats on the way there.

Latest Test: (2 hours spacing)
- Left the drivers heat on for a few hours....battery wasn't dead (seat was cold)
- Turned off the drivers, and turned on the passenger heated seat....still, battery is find. (seat was cold)
- Turned on heated mirrors, and car started

Does the seats have any type of occupancy switch that allows the heat to stay on, or remain off, until occupied?

Is there any known problem that could be causing this?

THANKS IN ADVANCE

STEVE
 

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I've never heard of heated seats killing the battery but I have two other suggestions:

There is a recall out for the fuel pump control module which according to the TSB can remain on after the car is shut off, thus draining the battery.

Also, the fan control module (radiator fan) can also malfunction and remain on after the car is shut off.

Have you listened for any humming around the engine bay after the is shut off for a while?

Sent from my LG-H872 using Tapatalk
 

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I had an issue with a draining battery as well, and the battery was only 3 months old at the time I started having the issues. The culprit turned out to be the new radio I put in, the new touch screen isn’t compatible with XM radio, therefore the XM radio line was just pulling my new battery down. The shop pulled the cable to the xm since it wasn’t usable and now everything is fine!!
 
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