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Discussion Starter · #1 ·
Greetings,

I own a 2001 VW Passat V6 with approximately 180k miles on it. I've been having an electrical issue for about 4 months that has cost me a small fortune and I still haven't been able to resolve the issue. In August, I had a new radio installed in the vehicle by Best Buy, which is when all the problems started. When the car sits for 4-7 days, the battery completely dies.

At first, I took the vehicle back to Best buy, and they tested the radio for a draw and the test came back negative. They could not find any draw when the car is turned off. They tested it in front of me by sliding the car stereo out and hooking a multimeter up to the radio wiring.

I took the vehicle to a mechanic (mentioning that it all started with the car radio) and they said that it had to be a bad Battery. I replaced the battery and still the problem persisted...

When I brought it back to the shop, they test it and could not find any draw on the battery at all when the car was off. They said that the alternator is the culprit. So they replaced the alternator, and I have been driving the car around without any problems for almsot 10 days before the problem came back. My car is dead again..

There seems to be a mystery draw on the battery and nobody can seem to figure out where it is coming from... I've spent almost 2k between dianosing the issue, repairs, tows, etc. and it's driving me nuts. What could be causing my car to continously drain the battery? I'm baffled by the problem and that nobody seems to know what is causing the issue.
 

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In August, I had a new radio installed in the vehicle by Best Buy, which is when all the problems started. When the car sits for 4-7 days, the battery completely dies.
It is very likely that they have caused the problem.


When I brought it back to the shop, they test it and could not find any draw on the battery at all when the car was off. They said that the alternator is the culprit. So they replaced the alternator, and I have been driving the car around without any problems for almsot 10 days before the problem came back. My car is dead again.
They didn't test it correctly, there is always some drain, they should have told you how much drain there was.
Get it checked by someone who knows how to check it.

If it does test within normal range when properly checked, you could have an intermittent fault, which may not be easy to locate.
 

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All problems such as this should be solved with this strategy: process of elimination. You start with what moves the electric current, the battery, and go from there, disconnecting anything electrically-powered until the current stops (interrupting the circuit by removing fuses is the usual way). There are only a limited number of circuits on a Passat; hard to believe that $2,000 could be spent chasing the faulty one.

If the problems started with the radio, as Tom said that is likely where the problem is. Have you ever had the car scanned for fault codes with that radio installed? An improper installation can short one of the diagnostic bus wires instead of leaving it "floating", drawing continuous current.
 

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disconnect the head unit and wait a couple of days. my guess is they swapped the two power leads. one is for the internal settings on the head unit (usually orange), and the other is for main power (usually red or yellow).
 

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You first need to establish whether or not you have a parasitic drain. Check what the actual current is,
if not within specs it was most likely caused by the radio install.

But it could be coincidence, and might be a faulty battery or a fault in the charging system. (I know you had the battery and alternator replaced)
 

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I agree 100% with what the others have said. More than likely the Best Buy donkeys are to blame.

By any chance are you using amplifiers?
I've seen the remote turn on for the amplifiers get hooked up with a constant "hot" wire which will keep the amps on all the time, that will drain a battery.

This is way off base, but some years back somebody in here had a simular problem after having the car worked on.
Turns out the heated mirror switched was messed with and the heated mirrors never turned off, hence draining the battery.
 

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I've been in this same situation and was told to check the battery and alternator. So far, I did have a bad battery but still have a drain. See this post parasitic-drain-battery-linked-fuse-14-37

I used a multimeter in 10A mode in between the negative post and a ground while the battery had a significant charge to determine the pull against the battery while the vehicle was turned off, key removed, and all doors shut (wait a bit for the CCM to go to sleep). If the pull is more than 0.05A or 50mA when the car is off and CCM asleep, that is suggested as being excessive. If the CCM is running, it's been indicated that up to 750mA may be normal until it sleeps.

Once I determined something excessive is pulling against the battery, I setup my multimeter against my windshield and went to the fuse box. One by one, I pulled each fuse and placed it back until the voltage dropped. Once I have found the fuses involved, I looked up what components are associated with that circuit and moved backwards across that circuit until I've found the component involved.

In all cases involved, Radio and CCM are usual suspects I've seen in various threads. You should try to pull a code, VAG-COM sometimes can be very useful in indicating if there is an open circuit and whether its to B+ or ground.
 

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There are several posts on here about a drain on the battery after installing a new head unit. Most determine the drain is coming from the Monsoon amp in the trunk and put in some type of relay. Did you have a Monsoon stereo to begin with? If so, do a search for Monsoon stereo and enjoy. I've been reading up on the stereo install in preparation for one I will be doing.
 

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+1 on aftermarket head unit with Monsoon amp. I've seen a few with this problem.

Pulling fuses is not the correct way to test drain, as some modules pull high current until they go to sleep. VW says to measure voltage drop across fuse, with the fuse plugged in. You can probably try the pulling fuses method, too, but you need to wait for the module to go to sleep again.
 

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I recall reading in VW bulletin that they don't recommend testing by pulling fuses for reason you mentioned and they provide methodology for testing to this effect also I believe...In troubleshooting my own issues, I came across multiple sets of people who was able to trace back their parasitic drain to a monsoon amp.
 

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Discussion Starter · #11 ·
Greetings,

Update on the status of the vehicle: It's been in the shop since December 27th and they are not able to find what is draining the battery.

They are telling me now that it must be a bad battery, but I replaced the battery 2 weeks before it went back into the shop, so it's only a month and 1/2 old, so I don't think that is the issue. The problem started when I had the new radio installed, however, they are not able to find a draw coming from the radio.

The vehicle did have the original radio in it previously (which I threw away as soon as I had the new radio installed), it looks like it might have been a monsoon according to the google search images I found. The car does not have subwoofers or amps or anything.

I just can't believe that nobody can find what is causing the drain.
 

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To reiterate what others have said, disconnect the new radio and see if the problem goes away.

Have you looked to see if the car had the monsoon system? The amp should still be in place, so just look for a shoebox-ish sized black box in the trunk, under the hat shelf. If it's there, then I can almost certainly guarantee that the issue is with the aftermarket radio not allowing the amp to turn off. The amp does not have a remote switch lead, it just "listens" for sound on a certain input channel and turns on accordingly. Several aftermarket HU's have a cheaply designed output stage, which will cause the amp to always think it's got signal from the HU, even when the HU is powered off. I am almost 100% certain that this is your issue.

Whoever is doing the tests on your vehicle clearly do not know what they are doing. These cars ALWAYS have some electrical draw (for the alarm, keyless entry, etc.), so if they're not finding any draw with the car off, they are doing it wrong.

What shop is your car at? If it's at Best Buy, I'd simply tell them to remove everything that they installed, and give you a full refund. They are notorious for extremely shoddy work, and there is absolutely no way that they have any clue on how to properly diagnose the issue.
 

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Discussion Starter · #13 ·
I'll have to call the shop and ask them to check for the Amp in the trunk. If there is one there, would you recommend disconnecting the amp or replacing the HU?
 

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They are telling me now that it must be a bad battery, but I replaced the battery 2 weeks before it went back into the shop, so it's only a month and 1/2 old, so I don't think that is the issue.
So the proof of that is simple: disconnect the battery, and if dead in 4~7 days, they were right. But I'll bet this could be solved with an Ammeter, or just a test bulb in series with the battery.
 

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I'll have to call the shop and ask them to check for the Amp in the trunk. If there is one there, would you recommend disconnecting the amp or replacing the HU?
First, try just pulling all the plugs on the Monsoon amp. When I was installing car stereos, a common complaint was battery draw from an external amplifier. Either they'd wired an amp to an always-on power supply, or the relay in the amp that turns it on and off was bad.

IIRC, the Monsoon amp switches itself on when it sees voltage on the input leads. It could be staying on because the head unit keeps something on those lines even when off; because of bad design, defect, or incorrect installation.

I like the idea of having Best Buy remove everything and start over elsewhere (they're idiots) but I shudder at the state they'd leave your car in while doing so.
 

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Discussion Starter · #16 ·
Another update, my car is still in the shop. I am picking up on Friday finally. I told them about the Monsoon AMP and they said that they tested it and did not find any drain. They are going to replace the battery with an Interstate Battery and are "confident" that will resolve the problem. Keep in mind that I just replaced the battery 2 weeks before it went back into the shop after being told it was a battery issue.

It doesn't make sense that it would be the Battery. How is it possible that they are not able to find this mysterious drain on the car? It's a very well known, reputable Auto shop that is servicing my vehicle...
 

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It doesn't make sense that it would be the Battery. How is it possible that they are not able to find this mysterious drain on the car?
I don't know why they can't find the problem- perhaps they never tried the ideas that I suggested on the 23rd. Let me explain another way: if this new battery is defective and self-discharges, it should do this whether in the car or on a workbench. Another thing to consider; my Daughter's 3.0 A4 had a weak battery in the morning on a couple of occasions, and it turned out to be the brake light switch. The brake lights would come on during the night, and drain the battery down.
 

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Any new part can be defective. Matter of fact, if something crops up, whatever I replaced last is the first suspect. But in this case, you've already replaced the battery twice, which puts the chances of it being the problem down below the noise floor. Does the shop proposing this know it was replaced before?

(Heh...) Have you tried closing yourself in the trunk? Sounds stupid, but three times over the years I've discovered a defective trunk light switch was the cause of a battery drain.
 

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I just went through this same thing with my B5.5 2.8L GLX 4Motion. I had no problems with my battery, installed an aftermarket HU and all of sudden my battery started lagging and finally died. Having read up extensively on issues with the Monsoon amp and aftermarket stereos, I was prepared for this. I wired a 12V SPST Automotive relay between the constant 12v power to my amp and then ran a wire to my remote on line from my amp to control the relay. On the green plug on the back of the amp there are three brown wires with red stripes that eventually become on big brown wire with a red stripe. This is the constant 12v to your amp. Cut the big wire and then wire Pin 87 on the relay to the side going to your amp and Pin 30 to the other end of the constant power. Pin 85 goes to ground and Pin 86 goes to the remote turn on wire from your head unit. I wired mine to one of the existing wires that went to my 6 disc changer, only because I didn't want to run another wire the full length of my car when I had a perfectly good one already in place. You will need to use 12 or 10 gauge wire for the power to your amp, and 16 or 18 for the ground and remote turn on. Once I figured out my approach for this it took me maybe 45 minutes to get the relay in place, and most of that was due to having to literally lie down in my trunk to get at the amp. Hopefully this helps you out and best of luck.
 

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Discussion Starter · #20 ·
I wanted to wait a couple weeks to make sure that the problem was fixed before posting an update. It's now been over a month since I had the amp disconnected and the mystery drain is no more. The mechanics could not figure it out and I don't know how long I would have had to go without a vehicle. Thank you all for the assistance with this issue.
 
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