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Discussion Starter · #1 ·
Greetings to all. Am at wits end. Have a 2003 NB with the 1.8T AWV. Car has a constant battery drain. In the past month have replaced battery, fuse panel above battery (with $150 factory part), aux cooling pump, alternator and have fabricated new alternator lead. With negative cable removed from battery and multimeter placed in series between battery and cable, car reads parasitic draw of 26 milliamps, well within VW specs. If car is left to sit battery will drain within 36 hours. If alternator cable is disconnected from S177, battery will not drain and car will be fine. Removed alternator and local parts store tested bad, hence why it was replaced. New alternator tested good yet problem still exists. Removed new alternator and battery and brought to different store for testing. Alternator and battery test good. Fabricated new alternator lead from 04 gauge marine grade wire. Cable resistance now reads .001ohms and with car running voltage drop test from alternator to positive battery post reads 0.118vdc. pretty low in my opinion and well within most specifications I've seen. In this condition, if I allow car to sit with all wires connected battery will drain within 36 hours. If Alternator lead is disconnected battery will not drain. Have reached a stopping point, am now at a loss. Any help or suggestions are greatly appreciated.
 

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.001

.001 ohms is the resistance of the cable end to end? You need to measure both ends (once disconnected) of that cable to ground chassis and see what ohms you get if any. It should be infinite resistance, if not than you might have a partial short somewhere's pulling down your battery over night. The other thing that is parallel to that wire would be the starter and it's solenoids.
 

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I believe he is talking about the cable from the battery to the alternator, it should be near 0 ohms. This is a non-issue.

Not sure if this will be much use, that circuit is very simple. ECU commands the alternator to charge, gauge cluster is ensuring the system is charging.


0.02A of draw shouldn't kill the battery that quick, I'm wondering if there is an intermittent component turning something on/off when the car is sitting. Or the alternator intermittently charging the battery when driving allowing the battery to lose it's charge gradually.

Besides a bad part (Partially shorted battery/alternator/voltage regulator), or a faulty ground (Under the battery is a common corrosion issue) not sure where else to look. Sounds like you handled troubleshooting the wiring quite well unless something was overlooked/damaged.

Out of curiosity, have you measured battery voltage when it's drained to see what it's at.
 

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cable

yea I know he meant the alternator cable and he measured it end to end at .001 ohms I believe. I think he needs to measure each end of that cable to chassis ground, while the cable end is disconnected of course. The reason I suggested that is because he claimed the battery does not drain when this cable is disconnected.
 

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Discussion Starter · #5 ·
thank you for the reply and the schematic. I have a lot more measurements but didn't want to overwhelm in the initial posting. From a fully charged battery (out of the car, on a charger) after 36 hours battery voltage was 10.4 and lights would only flicker. Yes the cable I referred to is the alternator lead which I made from 04gauge marine wire and its run independent of the harness so I know its not grounded or shorted to any other wires. I checked the ground connector under the battery but did not remove it to clean it. A negative voltage drop test from the alternator case to the batt NEG post (car running) showed only .116 vdc which was well within the tolerances I had found so I presume that ground to be ok. thanks again for the assistance.
 

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Discussion Starter · #6 ·
yea I know he meant the alternator cable and he measured it end to end at .001 ohms I believe. I think he needs to measure each end of that cable to chassis ground, while the cable end is disconnected of course. The reason I suggested that is because he claimed the battery does not drain when this cable is disconnected.

I made new wire and ran it independent of harness. I know this wire is good. Funny thing though, this car is the EXACT of your Avatar. I suppose you're familiar with it. Thanks for the assistance.
 

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I took a look at the wiring diagram for a 2002 AWV. Assuming it is the same as your 2003 wiring, the only things connected to the alternator are the instrument panel and the ECM. There should be connectors / wires from the alternator to both those components. I suggest that you test each of these one by one to determine what is draining the battery. First disconnect the ECM and instrument panel connections and see if the alternator drains the battery by itself. Then connect the ECM (brown/red wire) and see if that causes a drain. Finally, connect the instrument panel wire (blue) while the ECM is disconnected and check for battery drain. If this works, it should show exactly which component is causing the drain. Good luck!
 

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Discussion Starter · #8 ·
I took a look at the wiring diagram for a 2002 AWV. Assuming it is the same as your 2003 wiring, the only things connected to the alternator are the instrument panel and the ECM. There should be connectors / wires from the alternator to both those components. I suggest that you test each of these one by one to determine what is draining the battery. First disconnect the ECM and instrument panel connections and see if the alternator drains the battery by itself. Then connect the ECM (brown/red wire) and see if that causes a drain. Finally, connect the instrument panel wire (blue) while the ECM is disconnected and check for battery drain. If this works, it should show exactly which component is causing the drain. Good luck!
thanks for the assist!
 
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