Voltage loss

[regal7point5]

I am pulling my hair out trying to chase down a voltage loss or short or amp draw...not really sure what it would technically be called. I have a brand new battery as of a month ago, in which the old battery truly was bad. The car has run great for the last month, and now it just won't hold a charge...just sitting still. I will fully charge the battery and it will read just under 13V steady for a few hours.

It fully charged by 5pm yesterday to just over 13V...it settled and held 12.7 to 12.8V until 7am this morning. When I got home this afternoon...BOOM 3.7 volts and I could watch the voltmeter slowly "counting down". I posted yesterday about a mystery plastic part that was laying under the car...it was the starter post cover. Popped it on and hasnt made a difference in holding or loosing charge.

I have visually inspected and tested resistance through the box on top of the battery...and nothing is melted or out of whack that I can tell. One other weird thing; when the voltage was where it needed to be, the auto-window-crack feature was wonky. It would drop the window down, but put it right back up. Once the voltage nosedives, the windows do what they should. Even at 3 to 4V the cluster LED's work ok, but obviously it won't crank, headlights won't come on etc.

Any thoughts...I am about to set fire to it.

[brendan_TT]

I'm not an expert, and very new to the TT also. Do you think that maybe the window motor is somehow staying on? Like as if you held the window button in the up position, it would still be drawing juice?

I thought I read in my owners manual that it could be reprogrammed. If so, maybe try that?

[Mantvis]

When your try to close the windows from fully open, does it stop at some points, and you have to press the button again? Or no problem with that?

[Charlie_M]

Any thoughts...I am about to set fire to it.

Maybe the car will take care of that for you ... Shorts are dangerous!

I'm guessing the battery discharges with the car just sitting in the garage, right? If it discharges while you are driving, then replace your alternator.

First, if your battery really is down to 3.7V, it's probably shot. Disconnect the cables, charge the battery on a trickle, and have it load tested. May need a new one already.

Next, once you have a good battery again, hook the cables back up. Assuming you have a DVM, check how the battery voltage changes when you make the connection. If you do have a short somewhere, you should see the voltage drop.

Now leave the DVM connected to the battery and have a buddy watch it while you start pulling fuses, one at a time, then putting them back in. When you pull the fuse that is drawing current, the battery voltage should start coming back up slightly and drop again when you put the fuse back in. Don't forget the ones on top of the battery too.

Testing would be easier & more accurate with an ammeter, but I'm assuming you don't have one ....

[AudiMick]

So in 10 hours or so you dropped to 4 volts or so.

A normal average fully charged battery can drive about 50 amps for one hour. It's more complicated than that but that's the simple answer.

So you have probably about a 5-6 amp draw. About 60 watts.

When the car is sitting there doors closed key out it should go into standby and draw less than 50mA (600mW).

Get a good ammeter, one that can read 10amps Dc or so, disconnect the red battery cable. Put the meter in series with the battery and monitor the current. What ever you do don't try to start the car (turn it over) as that will blow the meter.

Then start pulling fuses from the panel till you find the one with the high draw.

Common problems are things are aftermarket head units, amplifiers and powered subs. In addition the electric cooling fans stay on.60 watts is a lot so it's not anything like an interior light.

Once you find the circuit it should be easier to fix. Maybe remove the circuit fuse overnight.

Good luck.

[Subverter]

Same thing happened to me after I installed an after market radio. It turns out that one the amps from the Bose system was constantly on. I changed the battery after testing it and it kept doing the same thing, then I tested the alternator and it was not producing the proper voltage so I changed it thought I had fixed it I went to drive the car the following week end and it was dead. I ended up uninstalling the head unit I had installed recently and that did the trick. I traced it to the rear amp on the passenger side. Hope this helps.

[regal7point5]

To further complicate things....

The battery read 3.7V on the DVM, but the car started easily...that should not have happened. Tested voltage when running at the battery and it was in the 14's. The reading at the alternator post was low 15's. I drove the car to work today to see what it does.

Either my DVM (decent-quality Fluke meter) is bugging out...or my car is possessed.

FYI, the windows operate 100% correct now. They drop and rise correctly when opening the door. They also do the auto up/down, unless you hit the switch again to stop/interrupt.

I have the stock stereo/amp/etc...but it is in safe mode currently. Actually it has been since I changed the battery a month ago, so I have possibly ruled out the audio circuits...unless somehow being in safe mode could drain the battery. The only other thing "not factory" was the fact that when all these issues were going on, my main cooling fan was electrically disconnected. I tested the motor and it was fried, so I disconnected it to avoid possible current drain. What happened is exactly the opposite...not sure if this is related.

[Mantvis]

Maybe the car will take care of that for you ... Shorts are dangerous!

I'm guessing the battery discharges with the car just sitting in the garage, right? If it discharges while you are driving, then replace your alternator.

First, if your battery really is down to 3.7V, it's probably shot. Disconnect the cables, charge the battery on a trickle, and have it load tested. May need a new one already.

Next, once you have a good battery again, hook the cables back up. Assuming you have a DVM, check how the battery voltage changes when you make the connection. If you do have a short somewhere, you should see the voltage drop.

Now leave the DVM connected to the battery and have a buddy watch it while you start pulling fuses, one at a time, then putting them back in. When you pull the fuse that is drawing current, the battery voltage should start coming back up slightly and drop again when you put the fuse back in. Don't forget the ones on top of the battery too.

Testing would be easier & more accurate with an ammeter, but I'm assuming you don't have one ....

Make connection to what? im trying to solve a mistery on my TT too lol
Battery is dead after 36hours of sitting still in the garage, i cant even start it. And it does have anew battery.

[ttwsm]

I think he means when you connect the battery back up.

[Mantvis]

is there anyway i can use voltmeter to check if im loosing voltage somewhere?
Like ive said after about 36hrs car can barely start it, so i know im loosing power somewhere.
Where do i start to check, how do i check?

[Charlie_M]

is there anyway i can use voltmeter to check if im loosing voltage somewhere?
Like ive said after about 36hrs car can barely start it, so i know im loosing power somewhere.
Where do i start to check, how do i check?

Read my post (#4 in this thread) if you want to go ghetto without an ammeter. Best way by far is to get an ammeter and use the tips from AudiMick's post (#5 in this thread).

Trying to trace an electrical problem without a DVM / ammeter is like trying to change a timing belt with a just a screwdriver.

[Mantvis]

Read my post (#4 in this thread) if you want to go ghetto without an ammeter. Best way by far is to get an ammeter and use the tips from AudiMick's post (#5 in this thread).

Trying to trace an electrical problem without a DVM / ammeter is like trying to change a timing belt with a just a screwdriver.

Yeah thats what i ment with voltmeter, i tought that DVM was something different. Guess not!

[regal7point5]

So the TT is acting up again with the same problem as originally posted. I charged the battery and drove the car to the Advance Auto where I bought the battery. They tested it and it showed OK at well over 500CCA...the battery is rated at 525CCA. They did a "full system test" with their mystery box which included a "parasitic drain" test. Everything came back as checking out OK. They said 0.00V parasitic loss...not sure how exactly it determined that, but it appeared to have some sort of ammeter I suppose that was looped around the ground wire, similar to a timing light. I assume it was measuring current through the wire, comparing it to the alligator clamps on the posts.

At any rate, I talked to a friend of mine at a VW dealership and he suggested the fuse box on top of the battery. I know they are problem prone, but I dont want to fork out $140 for a new box, and mine doesnt show any signs of melting. "Fuse-pull" testing to commence tomorrow...will report back in hopes of fixing it or helping someone else out too.

[regal7point5]

One other thought....could the alternator test out OK for charging, but somehow drain power when at rest? After digging through some of the 1.8T forum threads, it looks like a few folks have run into that.

[Mantvis]

So the TT is acting up again with the same problem as originally posted. I charged the battery and drove the car to the Advance Auto where I bought the battery. They tested it and it showed OK at well over 500CCA...the battery is rated at 525CCA. They did a "full system test" with their mystery box which included a "parasitic drain" test. Everything came back as checking out OK. They said 0.00V parasitic loss...not sure how exactly it determined that, but it appeared to have some sort of ammeter I suppose that was looped around the ground wire, similar to a timing light. I assume it was measuring current through the wire, comparing it to the alligator clamps on the posts.

At any rate, I talked to a friend of mine at a VW dealership and he suggested the fuse box on top of the battery. I know they are problem prone, but I dont want to fork out $140 for a new box, and mine doesnt show any signs of melting. "Fuse-pull" testing to commence tomorrow...will report back in hopes of fixing it or helping someone else out too.

Did it cost to hook up that mistery box? Also does any one know how accurate it is?

[regal7point5]

Did it cost to hook up that mistery box? Also does any one know how accurate it is?

No cost...just like when they do diagnostic scans. I have vagcom so I just scan myself. Anyway to do any troubleshooting through vagcom possibly?

Not sure how accurate the mystery box is...my guess is that it does load testing of the alternator and simply checks voltage and CCA.

[regal7point5]

Here are the printouts....

[Charlie_M]

So the TT is acting up again with the same problem as originally posted. I charged the battery and drove the car to the Advance Auto where I bought the battery. They tested it and it showed OK at well over 500CCA...the battery is rated at 525CCA. They did a "full system test" with their mystery box which included a "parasitic drain" test. Everything came back as checking out OK. They said 0.00V parasitic loss...not sure how exactly it determined that, but it appeared to have some sort of ammeter I suppose that was looped around the ground wire, similar to a timing light. I assume it was measuring current through the wire, comparing it to the alligator clamps on the posts.

At any rate, I talked to a friend of mine at a VW dealership and he suggested the fuse box on top of the battery. I know they are problem prone, but I dont want to fork out $140 for a new box, and mine doesnt show any signs of melting. "Fuse-pull" testing to commence tomorrow...will report back in hopes of fixing it or helping someone else out too.

You can buy a nice ammeter that clamps a loop around the wire you want to measure. A few DVMs (digital voltmeters) have them built in, or you can buy just the loop part that plugs into a DVM if you already have one. That is probably what they used, but then they should have reported 0.0 Amps parasitic loss, not volts.

Not sure how much I'd trust them; according to them you should have no problems.

Can we assume you have cleaned and re-attached all of the grounding points? Grounding strap to the motor is OK?

[regal7point5]

You can buy a nice ammeter that clamps a loop around the wire you want to measure. A few DVMs (digital voltmeters) have them built in, or you can buy just the loop part that plugs into a DVM if you already have one. That is probably what they used, but then they should have reported 0.0 Amps parasitic loss, not volts.

Not sure how much I'd trust them; according to them you should have no problems.

Can we assume you have cleaned and re-attached all of the grounding points? Grounding strap to the motor is OK?

Yes it actually was 0.00A...not volts, sorry I mistyped. See picture in previous post...sorry it is upside down, photobucket is goofy.

I have a Fluke and I *think* my brother may have the clamp attachment in his work tools.

[regal7point5]

Goodness, this thing is really irking me. I woke up at 5:30 to start doing the fuse pull method before work...darn multimeter's battery died!! The good news is, I do have the tool to solve the problem. I did spend about 45 minutes, but I couldnt figure out why the values were jumping all around, without even pulling fuses...then the screen faded and battery was dead. Hope to solve this today or tomorrow and hopefully help someone else out there!

[AudiMick]

The clamp on ammeters are not known for their accuracy when reading milliamps.

You need the meter in line to measure low currents like that.

[Charlie_M]

The clamp on ammeters are not known for their accuracy when reading milliamps.

You need the meter in line to measure low currents like that.

Maybe ... depends on the meter or external clamp accessory. Then again, he should be seeing amps; milliamp draws won't take the battery down to 4 V in 10 hours or so.

[regal7point5]

So I hooked it up in series....

Once everything stabilizes, it reads .027A at rest. This is 27mA right? When I open the door, it jumps to .300A, then settles to .150A. There were only 2 or 3 of any of the fuses pulled that made any difference. The radio, .002A; the instrument cluster, .005A, and fuse #38 at .100A. These were all measured drops in amp draw. If i remove #38 and close the door and let it settle it is actually higher at .033A, versus leaving all fuses in and letting it stabilize. Also, if I disconnect the second fuse on the battery top box, it goes to basically 0, but nothing really works with this disconnected.

Is .027A draining my battery in 24 hours, and is this too much draw at rest?

Does fuse #38 have anything to do with my problem. It is labeled luggage compartment light/central locking system. Funny thing is, my main interior overhead light works intermittently and the rear "trunk" light will only come on if the hatch is open.

What should I test for next?

[Charlie_M]

Is .027A draining my battery in 24 hours, and is this too much draw at rest?

What should I test for next?

No, and no. 27mA is tiny, your battery should be able to do that for months no problem. So you found no drain, just like AutoZone did, which means something else is going on.

I think your window problem is a red herring. The real problem is that it won't start, right? That tells me you have a problem with high current draw. Next time it won't start, take a jumper cable and jump *only* from the battery negative terminal to somewhere on the bellhousing. If it starts, then you need to fix the grounding strap to the motor.

Also, when you measure voltage, put your meter leads directly on the posts of the battery, not the terminal clamps. If you were really seeing 3.7V at the battery, I don't think your cluster lights would come on. Where were the test leads when you saw the 3.7V?

[gearheadzTV]

my main interior overhead light works intermittently and the rear "trunk" light will only come on if the hatch is open.

What should I test for next?

subscribed! I've been having the exact same issue just that now the interior lights don't work at all, trunk lights up upon opening the hatch. Motion sensor is no longer working either...

Have you redone your headliner? My problems all started around the same time I had a new sound system installed and the headliner repaired.

Took the car to the dealer and they couldn't figure it out, wanted me to pay for 8 hrs of labor to see if they could figure it out....I said

Please keep us updated, I got the if you nail this one.

[AudiMick]

Maybe ... depends on the meter or external clamp accessory. Then again, he should be seeing amps; milliamp draws won't take the battery down to 4 V in 10 hours or so.

Agree with that, I don't think the OP has really confirmed what the actual current drain is. But it should be at least 4 amps but he has never measured that.

IMHO once the current is under an amp clamping around a stranded 4 or 8 gauge wire is pretty iffy. I have seen it off by 50%, and your typical parts store guys don't know that.

[regal7point5]

No, and no. 27mA is tiny, your battery should be able to do that for months no problem. So you found no drain, just like AutoZone did, which means something else is going on.

I think your window problem is a red herring. The real problem is that it won't start, right? That tells me you have a problem with high current draw. Next time it won't start, take a jumper cable and jump *only* from the battery negative terminal to somewhere on the bellhousing. If it starts, then you need to fix the grounding strap to the motor.

Also, when you measure voltage, put your meter leads directly on the posts of the battery, not the terminal clamps. If you were really seeing 3.7V at the battery, I don't think your cluster lights would come on. Where were the test leads when you saw the 3.7V?

The windows have never been a problem...except when I had the dead battery, which is completely understandable. The 3.7 was measured directly on the battery posts, but I suspect that reading may have been skewed as it was right before the DVM 9v battery died. Last night I did probe the battery terminals and it was reading about 11.8v...this was after an overnight charge, then letting the terminals be connected for a while before working on it. I was able to see the voltage go down by .01v about every 10 seconds with the terminals connected.

Could the meter have been in the wrong scale? The probes are in the "10A" socket on the DVM and it is "x.xxx". I was measuring .3A and lower, worst case scenario. It would "OL", overload, but only when I would open the door and the window would crack up/down, but that was expected. I will check grounding points next...

[Mantvis]

The windows have never been a problem...except when I had the dead battery, which is completely understandable. The 3.7 was measured directly on the battery posts, but I suspect that reading may have been skewed as it was right before the DVM 9v battery died. Last night I did probe the battery terminals and it was reading about 11.8v...this was after an overnight charge, then letting the terminals be connected for a while before working on it. I was able to see the voltage go down by .01v about every 10 seconds with the terminals connected.

Could the meter have been in the wrong scale? The probes are in the "10A" socket on the DVM and it is "x.xxx". I was measuring .3A and lower, worst case scenario. It would "OL", overload, but only when I would open the door and the window would crack up/down, but that was expected. I will check grounding points next...

Where are all the main ground point in a TT?

[regal7point5]

I did remove the crossover pipe as it is relatively unnecessary and makes oil changes harder. I didnt see any grounds straps tied into this...but could there be?

[Mantvis]

I did remove the crossover pipe as it is relatively unnecessary and makes oil changes harder. I didnt see any grounds straps tied into this...but could there be?

Wouldnt it make the car "squat" in the front by removing the bar? it ads more stability to the whole frame. IDK personaly i dont see a reason why to remove it.

[regal7point5]

Well...I THINK I have it figured out for now. I yanked and fully removed the rear trunk/luggage light; the one in the trunk on the driver side. The light never stayed on when I closed the door, but it was the only thing on fuse #38 I could easily remove. Acutally removed and disconnected it aaaaand....

No more voltage loss. The battery has stayed at 12.15V for 2 or 3 days straight now. My only guess is that this portion of the wiring was shorting out somewhere, even though the light operated as it should. Could also possibly be the trunk sensor switch somehow. For now, I am just going to do without the trunk light. Hopefully this helps someone.