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Discussion Starter #1
The Alternator on my 2010 Frontier SE with a 4 cylinder Auto transmission will charge at
14.5 volts for a few minutes and then drop to 13.1 volts. Even if I turn the lights and AC
on it will not go back to 14 volts. If I turn the engine off and wait 15 minutes it will
charge at 14.5 volts again for a few minutes and then drop back to 13 volts. The battery is a 10 month old AC Delco and appears to be in good condition. Is this a failing alternator or
could there be some other cause.
 

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Sup Mod keeping the peace
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6,251 Posts
13.8 v is within the normal charging range. If you measure it right after you start the engine after the car sits overnight it might read in the 14’s, but should return to the 13.8 v range over time as the engine runs. It may be in your best interest to get the battery load tested; you can get it load tested at some auto parts stores for free.
 

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NF Mod/Nissan Master Tech
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There's probably nothing wrong with it. Late model Nissan charging systems are designed to use the ECM to control when and how much the alternator charges to help save gas by lessening the load on the engine. On the V6 models, there is a voltage sensor on the negative battery cable (it's about 10" from the battery cable end and looks like a plastic box that goes around the cable). I'm not sure if they do this on the 2.5L, but I do know on the Altimas with the 2.5L, the alternator has a built-in clutch to allow the pulley to freewheel when the alternator is not needed to charge. So, when it comes to testing the charging system, it's belt to consult the factory service manual for your vehicle. They good ol' simple days are gone!
 

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Discussion Starter #5
I not sure what is happening. Battery charges at 14.8 for a few minutes and then drops to
13.9. If I turn the lights and air conditioner on it drops down to 13.1. It will not come back
to 14 unless I turn the engine off and restart. The battery checks good on a load test. I do
a lot of short trip driving and as a result of this problem I eventually have to charge the battery.
I have another vehicle and it charges at 14 all the time at idle or at speed and it doesn't
change much when I turn the lights and AC on.
 

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Sup Mod keeping the peace
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6,251 Posts
According to the Factory Service Manual (FSM), the 4 cyl QR25DE engine in your vehicle uses the “power generation voltage variable controls.” that SMJ described. The FSM contains diagnostic procedures for trouble shooting the charging system. You can download a copy of the FSM from https://ownersmanuals2.com/. The CHG.PDF section is the one you need to read. You'll need a multimeter for testing. Good luck, let us know how you make out.
 
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