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Car is totally dead; battery is fine. How do I track down the problem?

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Old 04-10-2009, 01:54 PM   #1
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Default Car is totally dead; battery is fine. How do I track down the problem?

I checked the battery and it's perfectly fine (12.5V). When I turn the ignition, nothing happens at all (no lights, etc). This all happened after I started my car this morning and then it died one second later. Is it possible some kind of relay or fuse died?

Basically I would like someone to tell me a method for finding the problem? Normally I'm pretty reliant on my VagCOM, but no power = no output.
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Old 04-10-2009, 02:06 PM   #2
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You could check the fuse box for 12.5 volt to ground. I think if the central locking unit doesn't have power then the whole 12v system would be down. Same for the ECU.

There must be a Vbatt bus some where in the car, although I don't know where that would be... probably located by all the relays and close to the fuse box. I suspect it would be behind the knee bolster and behind all of the relays ect.

I really don't know much more than that. And I guessed on the location. But there must be a 12V bus bus that every thing ties to, maybe the cable has been broken loose from that.
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Old 04-10-2009, 03:41 PM   #3
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Might be your ignition switch. Check it if you can, after you have checked all your fuses.

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Old 04-10-2009, 03:48 PM   #4
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What would I check for on the ignition switch? I presume it's not as simple as taking it apart and ::whoa:: I will see what's wrong with it?
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Old 04-10-2009, 03:54 PM   #5
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If no fuses are blown is likely ignition switch. I do not know how to check the ignition switch. Might need to take it into a shop.

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Old 04-10-2009, 04:07 PM   #6
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You say "No power to the car" does this include keyless entry, trunk lights, lights as you open the door, clock and odometer??

If nothing works you should be able to rule out the switch.

If every thing works besides what is related to the switch, ie you can turn on the lights but the dash doesnt kick in beyond the odometer and clock when you open the door. Then the switch is the most probably culprit.
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Old 04-10-2009, 04:34 PM   #7
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Nope, nothing works... keyless entry, all lights, etc... so what now?
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Old 04-10-2009, 05:36 PM   #8
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Well its obviously not the ignition switch in that case. Interior lights are on an independent circuit vs the instument cluster and the locking unit. Power is not getting to the main 12V bus, or the main ground cable is not making contact with the chassis.


These bolts usually have 4 brown wires running away from them, I think there are some conventient ones located on the fire wall.

You shouild test for continuity from the battery terminal clamps. (ohm metering)

If you have continuity between the negative (-) battery terminal the chassis ground and continuity between positive (+) and the fuse box bus. Your problem could be a power cable that has failed...

I think this far uses 4 gauge wire, so it would be difficult for this to fail.. but maybe if your starter wouldn't dissengage or something I suppose it is possible...

Some where there is a master 12V bus, this is what feeds the fuse box and relays. It should have a direct connection to the batter, and some relayed connections to the alternator and starter. I think this is located behind the knee bolster as I stated earlier.
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Old 04-11-2009, 03:46 PM   #9
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^^^^^yup, what he said^^^
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Old 04-17-2009, 07:25 PM   #10
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Quote:
Originally Posted by NiceS4 View Post
I checked the battery and it's perfectly fine (12.5V). When I turn the ignition, nothing happens at all (no lights, etc). This all happened after I started my car this morning and then it died one second later. Is it possible some kind of relay or fuse died?

Basically I would like someone to tell me a method for finding the problem? Normally I'm pretty reliant on my VagCOM, but no power = no output.
What was the resolution to your issue?
My 2001 Audio TT is Dead. The right hand display says FUSE. I also checked all the fuses and the user manual nothing there.

Please help me out.

Thanks
Kirk
Dallas Texas USA
You can email me at guyindfw07@yahoo.com
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Old 04-23-2009, 12:10 PM   #11
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Quote:
Originally Posted by guyindfw07 View Post
What was the resolution to your issue?
My 2001 Audio TT is Dead. The right hand display says FUSE. I also checked all the fuses and the user manual nothing there.

Please help me out.

Thanks
Kirk
Dallas Texas USA
You can email me at guyindfw07@yahoo.com
You know, I still haven't fixed this problem. I tinkered with the wires in the main bus - basically removed and tightened them and I got the car started! But then the next morning I had the same problem. The car would start and then shut off right away. I'm really not sure what's going on at this point.
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Old 04-23-2009, 12:11 PM   #12
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By the way, what I say "shut off right away" - mean everything would be dead. No lights, ignition, anything.
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Old 04-23-2009, 12:15 PM   #13
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Damn, it's wierd that it worked but only for a little bit of time. Sure is acting screwy.

Last edited by complacentsee; 04-23-2009 at 12:20 PM.
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Old 04-23-2009, 12:29 PM   #14
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Damn, it's wierd that it worked but only for a little bit of time. Sure is acting screwy.
My absolute guess is that the cold weather in the morning made the contact points on the main bus contract and that's why the car would start and then die completely each time.

Maybe I should replace the bus or the leads/end points? It doesn't look like there's any infiltration...

Ideas ANYONE?
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Old 04-23-2009, 12:49 PM   #15
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My only sugestion is to start taking readings and figure out if its the bus, or the batter lines, or the terminals or where the issue really is.
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Old 04-24-2009, 07:28 AM   #16
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My only sugestion is to start taking readings and figure out if its the bus, or the batter lines, or the terminals or where the issue really is.
What kind of readings should I be looking for? Obviously 12.5 at the battery lines, but aside from that?
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Old 04-24-2009, 09:39 AM   #17
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I would remove the battery and start mesuring resistances myself. Big thick wires should have real low resistances. And as long as your talking about clean terminals all the measurments should be very low.

Neg terminal to grounding .
pos terminal to the 12 bus.

And I would go nuts and try combinations of locations bus to bus.

Battery should read mid 12Vs. low 12Vs and things should light up, but the battery is more or less dead.
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Old 04-24-2009, 11:02 AM   #18
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BTW where are you located. I might be able to help you out some time for use of your VAGCOM.
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Old 04-24-2009, 11:42 AM   #19
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BTW where are you located. I might be able to help you out some time for use of your VAGCOM.
I live in Astoria, NY and work in Bergen County (Allendale), NJ
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Old 04-24-2009, 11:44 AM   #20
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Originally Posted by complacentsee View Post
I would remove the battery and start mesuring resistances myself. Big thick wires should have real low resistances. And as long as your talking about clean terminals all the measurments should be very low.

Neg terminal to grounding .
pos terminal to the 12 bus.

And I would go nuts and try combinations of locations bus to bus.

Battery should read mid 12Vs. low 12Vs and things should light up, but the battery is more or less dead.
The resistances look pretty good.

You know, the weird thing is that the power is routed fine when I bend the second post from the left on the main bus toward myself (I just put a socket with extension over it and bend it very slightly toward myself)... And when I bend it back, everything cuts out...

Is it possible the relay on top of it is busted or something?
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Old 04-24-2009, 11:44 AM
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