Is My Alternator Going Bad?

[Fitz98]

My 2004 Nissan Sentra battery light flashes on and off occasionally.
It is very random and not very often, just blinks on for a brief moment every now and then. The volt meter is reading 14.4 volts at the terminals.
Is it possible the alternator is just staring to go bad, or should I look to diagnose something else?
I don't want to get stranded with a dead alternator...been there, done that...., but also don't want to waste money.

 

[Hall]

Keep the meter on for longer and monitor it. Someone correct me if I'm wrong but I think the output voltage can vary but should not drop below XX volts (i.e. 12.X volts or something).

How old is the belt ?

 

[JeffKeryk]

14.4v at idle if good. I am guessing you measured the voltage at idle...
How many miles? Those things don't last forever.
I would hit the lights, run the heater fan, radio, etc.
Try and tax it and then measure the output.

If you do replace it, make sure you get a quality alternator...
If your's is original, I would seek out a local rebuilder.

 

[JimPghPA]

1 ) In Florida, have the battery checked if it is 2 years old or older, preferably by a shop that actually has a big carbon pile resistor load tester that actually places a high current load on the battery that is selected to match the battery. Alternator rebuild shops that have been in existence for a long time are more likely to have this type of tester, compared to your average mechanic, or shops that have not been around for a long time.

2) Those same shops should be able to test the charging system.

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Alternators usually completely fail, not intermittently like you are describing. If the vehicles Voltage can not stay high enough when the RPMs are low, it usually is that the alternator can not keep up with the demand at those low RPMs because the battery is not doing its share of the work, and even may be draining too much from the alternator.

Battery life varies greatly. "In areas with hot climates like Florida, Arizona, Texas, and other VERY HOT AREAS, THEY CAN AND OFTEN DO, WEAR OUT IN AS LITLE AS 2 YEARS." In areas where the average ambient temperature is much cooler they can last a lot longer. in other words the average ambient temperature the battery sees over its life, greatly determines how long it will last. In general chemical reactions happen twice as fast if the temperature is raised by 10 degree C ( 18 degree F ) , and happen half as fast if lowered by 10 degree C ( 18 degree F ). An average ambient temperature change of only 10 C / 18 F over the life of a battery can drastically change how long the battery last.

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Another possibility with an older vehicle it is that the belt tensioner is not supplying the proper tension. And if that is the case the alternator may not be turning fast enough because both: the drive pulley from the engine that make the pulley move can slip some, and the pulley on the alternator can slip some. Combine both of those and the alternator ends up not turning fast enough to do its job even though there is nothing wrong with it.

 

[Fitz98]

I am pretty sure it is not original.
Wife said she had a mechanic replace it while I was working out of state several years ago.
Battery is a 10 month old interstate.
I will check the belt, tensioner and voltage under high loads

I am assuming the battery light would only come on if the charging voltage drops below a certain level, or does it measure/monitor anything from the battery as well?

 

[Dave9]

Definitely check the belt tensioner in case belt has stretched to the end of its effective range or spring is weak and it's slipping. Also check condition of belt, may be wearing fast if slipping.

It could even be corroded battery terminals or a poor ground. Check *everything*.

 

[JimPghPA]

If the vehicle was used to jump start another vehicle, AND the vehicles engine was running while the vehicle with dead battery was cranking or trying to crank, then under those conditions, the alternator of the good vehicle could have its alternator output diodes damaged when it puts out a lot of current to try to start the dead vehicle. This sometimes but rarely happens, because the starter of the dead vehicle and the dead battery of the bad vehicle, draws too much current. With modern alternators, that have pulse width voltage regulation this does not happen as often as it use to with older vehicles that had linear voltage regulators. But, still alternators do not have any circuitry to sense how much current they are putting out, and with very heavy loads like a starter cranking they can sometimes put out soooooo much current that they damage there output diodes.

So, was the vehicle used to jump start another?

 

[JMJNet]

Bring it to somewhere to LOAD test the battery (not voltage test).
The part store usually can do it.
In addition, they can go a step further to test the alternator.

 

[MasterSolenoid]

When my 'check engine' light came ON, the 'dummy' voltage gauge was also showing LOW.
I immediately went home and charged the battery.

But, I also plugged into the cigarette lighter a Voltage Meter,
while driving, I could see that the Alternator would 'occasionally' cut-out.

I replaced the Alternator and all was well.

https://www.amazon.com/Battery-Charging-Condition-Alternator-Display/dp/B07422ZPT4/ref=sr_1_7?crid=13FPMS2MMXPT0&dchild=1&keywords=dc+voltage+meter+tester+plug+in&qid=1634505124&sr=8-7

 

[Fitz98]

No jump starting

 

[Fitz98]

Is there any internal parts on the alternator that are not sealed and could be affected if they get wet?
It wasn't too long ago that I had to replace the radiator. It was leaking and spewing coolant under the hood. Maybe that had something to do with it.
Went to check the terminals on the alternator for corrosion, but will need to remove a metal bracket that is attached to the cooling fan housing. It will not let me get enough clearance to remove the alternator connector.

 

[Fitz98]

When my 'check engine' light came ON, the 'dummy' voltage gauge was also showing LOW.
I immediately went home and charged the battery.

But, I also plugged into the cigarette lighter a Voltage Meter,
while driving, I could see that the Alternator would 'occasionally' cut-out.

I replaced the Alternator and all was well.

https://www.amazon.com/Battery-Charging-Condition-Alternator-Display/dp/B07422ZPT4/ref=sr_1_7?crid=13FPMS2MMXPT0&dchild=1&keywords=dc+voltage+meter+tester+plug+in&qid=1634505124&sr=8-7

Looks like a good device for troubleshooting an intermittent problem

 

[Warstud]

Sometimes the bearing goes bad and affects charging and will get noisy.

 

[atikovi]

I don't want to get stranded with a dead alternator...been there, done that...., but also don't want to waste money.

You wont get stranded. You would have at least an hour to drive after it dies before the engine quits is you don't use headlights or other loads.

 

[Fitz98]

Just found receipt.
Alternator was 275.00 and replaced in 2015. Did not specify brand. Receipt said lifetime warranty on alternator, but the owner died and the shop closed.
Added 14K miles since then.
Both belts changed at same time...FWIW.

 

[mk378]

This is typical of the alternator brushes wearing down until they only intermittently touch the slip rings. The "battery" light is a self-check of the alternator. It's only going to light if the alternator is not turning or there is an internal problem in the alternator.

 

[Hootbro]

I assume this is an old school alternator and not part of a "smart" on demand battery charging system? If so, I suspect you have a rectifier diode on it's way out in the alternator. Auto Parts store bench testing may or may not catch it.

If the battery terminals are clean and the battery passes a load test, I would change the Alternator. I would also recommend get a OEM branded one and failing that, an actual new build alternator if going aftermarket.

 

[zzyzzx]

Alternators usually completely fail, not intermittently like you are describing.

If it's intermittent than the brushes are probably almost worn out. Check that first.

 

[zzyzzx]

Just found receipt.
Alternator was 275.00 and replaced in 2015. Did not specify brand. Receipt said lifetime warranty on alternator, but the owner died and the shop closed.
Added 14K miles since then.
Both belts changed at same time...FWIW.

Too bad. The Laurel, MD NAPA honored a warranty on an alternator I brought in with an 11 year old receipt.

 

[Hall]

while driving, I could see that the Alternator would 'occasionally' cut-out.

I know that Ford has been using a Battery Management System (BMS) for a few years and my understanding of that is that the alternator cycles on and off as needed. It does this to provide slight bumps in fuel economy which to mean suggests it has a "clutch" that engages or disengages the alternator pulley ( ). I don't know how it would reduce the load on the engine to help fuel economy otherwise. Anyway, a monitoring device might give false or misleading information in this case.