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Dying battery

3K views 17 replies 7 participants last post by  shurguywutt 
#1 ·
Can an alternator still be a problem even after a diode test checks out ok?
 
#2 ·
Yes. Slip rings and brushes can be worn out, giving intermittent service. The front bearing can wear out, causing noise and brush/slip ring failure. Rotor or stator windings can fail as well. Check system voltage with engine running and headlights on and heater fan on high to load system. Should be about 14.4 volts.
 
#7 ·
here's a short note on the your answer I just disconnected the ground wire from the battery and hook my voltmeter between that in the terminal the cable in the terminal and I'm getting full voltage to there so it does sound like a short but would anybody know what is causing it
 
#12 ·
All vehicles have a little drain happening with the key off. The vehicle computers stay awake, even when you don't. This could show up on your voltmeter as 12 volts, but it's meaningless. You need to get an ammeter to check the current flow. I think that 40 milliamps or so is ok. That is .040 of an ampere. If you are reading a half amp, or a full amp, then you have an excessive parasitic drain.
 
#8 ·
It can be anything from the PCM to a small light. Have the hood, trunk, doors and latches closed (use a screw driver to push in the latch so the car thinks the hood and doors are closed). Hook up your volt meter like how you described and pull the fuses one by one to see if any causes the volts to go down. That'll steer you in the direction of what it could be.
 
#13 ·
If you pulled the negative battery cable off of the battery then measured essentially between battery positive and chassis that is likely due to a charged capacitor. Wait a few minutes and see if you still read ~12Vdc.

The best way to measure where parasitic draw is coming from is to put the meter into milli volt mode and measure voltage across each fuse. The fuses with the highest voltage drops across them indicate those circuits which are drawing the highest current. You perform this measurement with the keys removed from the ignition. Leave the fuses installed when you measure.
 
#14 ·
I may have the same issue hence posting here instead of a new thread
During the pilot driving I can see in real time the voltage charge go as high as 13.8 volts then would drop 2 volts, every few minutes it would go as low as close to 11 volts under the 12v thresh hold. Then it would spike back up to the 13.8 v . Battery is coming up to 2 years Walmart brand . Alternator was swapped out at The 110k mark on the meter that was 80k or so. So this may be age creeping up on the Alernator.
 
#17 ·
During the pilot driving I can see in real time the voltage charge go as high as 13.8 volts then would drop 2 volts, every few minutes it would go as low as close to 11 volts under the 12v thresh hold. Then it would spike back up to the 13.8 v . Battery is coming up to 2 years Walmart brand . Alternator was swapped out at The 110k mark on the meter that was 80k or so. So this may be age creeping up on the Alernator.
Get a free alternator + battery test at auto parts store like Advance or Autozone. This can help confirm your own diagnosis. I know you're not fan of this device but my daughter texts me when it's less than 13.8 to 14.4 LOL
 

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