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2001 Pontiac Montana battery drains while car is turned off.

 
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awseightyfive awseightyfive
New User | Posts: 1 | Joined: 05/10
Posted: 05/20/10
09:16 AM

A couple months back I noticed my car battery was going bad. Had to jump it everyday ect. So after a month of this we put a new battery in it. In about a week the battery once again is doing the same thing. If I drive it all day it is fine but once I leave the car off for about 8 hours it will not turn over and if I let the car sit for 24 hours the battery is completely dead and nothing will turn on.
Once again this is a 2001 pontiac montana. Is this an alternator issue or something else? Confused  

waynep7122 waynep7122
Addict | Posts: 4561 | Joined: 08/09
Posted: 05/20/10
06:00 PM

several things...

you are going to need a digital volt meter ... that also has at least a 10 amp DC setting...

gator clips for the ends of the test leads... if it did not come with them...


first... set the volt meter to 20 volt DC scale...
measure the battery with the engine turned off...

if you have run the engine in the last 3 hours.. turn the head lights on for one minute.. then turn them off...

measure the battery voltage..

12.65 is a fully charged battery
12.45 is a half charged battery
12.25 is a quarter charged battery...

if your battery reads less than 12.45 volts.. it needs to be charged on a battery charger for at least one hour at 10 amps.........

now.. you can start the motor..   measure the battery voltage with the engine running.. with the fully charged battery...

the voltage with the engine running should be over 14.1 volts and probably close to 14.6 volts..

if you see this kind of voltage.. the alternator is working..

now... that you have verified.. the charging voltage...

with the volt meter still set to 20 volt DC scale...   engine running.. turn the head lights on also...

measure from the negative battery post to the engine block..  you should see a reading of 0.04 volts DC..

measure from the negative battery post to the body...          you should see a reading of 0,02 volts DC..

measure from the engine to the body...       you should see a reading of 0.02 volts...  if you have higher voltage .. you have a bad ground somewhere in that circuit...


now.. on to the parasitic draw test...

engine off.. drivers window down..  all lights off...

disconnect one side of the battery..   turn the digital volt meter to 10 or 15 amp DC setting..  you will have to replug one of the leads in the meter face..  then hook the amp meter across the gap you have made by unhooking one side of the battery...  one wire to the post... one wire to the disconnected terminal..

expected reading is 0.020 or 0.025 amps...  post what readings you get...  there are several computers onboard that need full time power.. there are several circuits that may draw power when the key is off.. when they have failed...  

i usually open the door.. pull the dome light fuse... see if the draw vanishes...

if it is still there.. start pulling the fuses one at a time... checking the draw... each time...

yes this is a LOT... print it.. go through it one step at a time.. this is exactly what i do when cars come into the shop...  

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