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Battery drain problem. Very annoying!

I have a 2002 VW GTI VR6 (MK4 24 valve, 88k miles) that has an occasional battery drain issue. It won’t be able to start after parking depending on outside temps. The warmer it is, the faster the drain. It first happened this past summer in ambient temps over 90 degrees and currently when it gets somewhat warm. It has not happened in freezing temps or less than, I’d say, 50 degrees. Yet.

I’ve taken it to a VW/Audi shop where they pulled just about every fuse and tested for drain but given its occasional nature, of course they didn’t find the source cause.

Any ideas? The fans that run after engine shutdown do turn off after a while.

Also, since that shop didn’t charge me for the diagnosis, I feel the need to give them a shoutout. Anyone in the Queens/Brooklyn area, check out Awesome service.

If the cooling fan circuit is causing the trouble then perhaps the coolant temperature sensor that turns the fans on is causing the problem.

Agree with @Cougar…it’s an intermittent problem so it will be tough to find. I have seen this problem before and that cooling fan will run down your battery over time. Replacing the sensor may be your best alternative. The fan relay may also be sticking so have that looked at as well.

@thephatness extreme temperatures can kill marginal batteries.

How old is that battery?
If it’s more than 5 years old, replace it

You need to take the vehicle to someone who can test for a parastic current draw when the temperature rises without disconnecting the battery. There are modules in the vehicle that can be effected by the temperature where they fail to go to sleep causing the battery to drain down. These are called FRED’s. Frustrating Ridiculous Electronic Device

If a module fails to go to sleep it can cause the battery to drain down.

You can read about FRED’s here.


Thanks for the info @Tester. Since "FRED’s are probably being added every year the list is growing. The “even sneakier” FRED’s are probably the worst culprits.

Thanks everyone.

The battery has been changed a few times and tested. The $4 battery disconnect solution is holding me over on the warmer days and has proven that the battery is charging well and holding it.

That’s an interesting article on FREDs. I’ve heard about sticky auto door locks as a possible culprit. Hopefully whichever one it is, it will be obvious on the voltmeter because it will drain the battery in a matter of hours!

When this was happening to my wife’s 2007 Ford 500, I couldn’t find the drain because it was intermittant. Something was staying on after the engine was shut down, but it wasn’t obvious, like a cooling fan or lights. Out of desperation, and figuring that one of the few things with a sufficient draw was the fuel pump, I switched the fuel pump relay with the headlights relay. My theory was that the relay was sticking on, but you wouldn’t necessarily hear it. But if the headlights stayed on, it would be obvious.

Anyway, since I switched the relays, the problem has not happened again. The relays are inside the box in the engine compartment on the front left fender.

PS - the Deborah who gave her '97 Tercel as a donation to Car Talk is my daughter. She showed this to all her her classes (she is a biology teacher) and told them that she is now “famous”.

If you have an aftermarket radio installed, that should be on your list of suspects. I just traced my recurring battery drain problem to an aftermarket stereo that draws power from a line connected straight to +12V, bypassing the ignition switch. My temporary fix was to find the right fuse, and pull it. Problem solved until I can rewire the stereo.