E420 Electrical problems - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 01-20-2009, 06:01 PM Thread Starter
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E420 Electrical problems

'97 E420. Battery drains after two days. I put in a new battery but still have the problem. Driving everyday it's fine. Started even at -12. Two days later dead again. Benz dealer say's they can't find anything wrong, "That'll be, hmmm, $150 please." Any suggestions on where to start looking? I'm considering putting in a battery disconnect but that's only a band-aid. Thanks in advance for your help!!
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post #2 of 5 (permalink) Old 01-20-2009, 09:14 PM
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Just from a general perspective, to guard against the possibility of bad replacement battery, and to confirm that some load is draining your battery over the two days, stick a 10A or higher rated ammeter (or multimeter set to ammeter mode) between the negative battery post and the negative battery cable. With the engine off, disconnect the negative terminal of the battery, and hook up an ammeter. Ensure that the polarity of the hook up is correct. The battery is located under the right rear seat (right side meaning opposite to the side of driver). Prior to taking the current reading, it would also be good to check the battery voltage while cranking and not cranking when the car's battery charge is not depleted.

Just curious, did you replace the battery yourself or did someone else do it for you?

Last edited by techyiam; 01-20-2009 at 10:47 PM.
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post #3 of 5 (permalink) Old 01-20-2009, 10:48 PM
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This could be anything, like misaligned door that doesn't close the switch and keeps sets computer active, or glove box lighth. Make a tester with big load, like 21 W light bullb, pull the fuses and staart testing where is the power draw. You need to start testing after the car goes into sleep mode -all lights and displays off.
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post #4 of 5 (permalink) Old 01-21-2009, 09:27 AM Thread Starter
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E420 Electrical problems

Battery tests good. Doors shut and no lights on.... will start pulling fuses when it warms up a bit in Indianapolis. Thanks for your help!
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post #5 of 5 (permalink) Old 01-22-2009, 12:58 PM
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Connect a multimeter between the positve pole on the battery and the cable set it to read over 10 amps . Check to see what draw is on the battery , it should be below .06 when the car has entered sleep mode . If the draw is greater start pulling fuses and check the reading on the multimeter to see witch circut has the current draw . This will help locate the source of the problem
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