Here's the status on my 2001 Maxima SE:

- When running,voltage reading across the battery posts is 11.9 (not the expected 14.5)

- No warning lights on the dash while running (i.e. no brake or battery light indicator displays)

- OK, I know I'm not suppose to do this, but couldn't help myself: I disconnected the battery while the car was running and the car kept running. Voltage across alternator (measured from the disconnected battery connectors) is 10.8 while the car is running.

So it looks like my alternator works well enough to keep the car running with no battery, but only outputs 10.8 volts (not the expected 14.5). Perhaps the voltage regulator is shot?

So I'm guessing it's time to replace the alternator unless I'm missing something here?

Thanks for any comments!

DJ

 

Both readings are low and probably indicate issues with the alternator.

And yes, it's not a great idea to do what you did.

At least you got a jump on things and can replace the alt before it ruins your battery. And it happened in the summer when it is a better ttime to work on it.

Before you jump and do teh jump do some searches and check the "How To " area. Pleanty of people have done it and it's better to find out about any pitfalls.

Good Luck.

 

What was the original problem? Why did you start to measure voltage in the first place?

I'd make sure that engine is at 1-1.5k rpm while measuring voltage.

Battery cannot produce volyage higher than what alternator produces so you have contradiction in your measurements. The only thing comes to mind is that voltage without battery had a lot of ripple and as voltmeter shows average voltage it averaged to 10.8 while picks could be much higher. I think this ripple is the reason why you're not supposed to disconnect battery on the running car.

Can you put your battery in another car and measure it there? It doesn't have to be Maxima ...

 

put the voltmeter on the alt. output wire and ground. if your readings are the same(they prob. will be), you need an alternator. looks like you caught it just in time. if the car starts i would assume(just assuming) that your battery is ok. i would check the static voltage after its charged for alittle while (on the new alternator).

 

Don't drive with your headlights on for too long... or bye bye battery.

Time for new alt

 

Be sure to read the factory service manual (FSM) procedure for both diagnosis and removal/replacement. You have to unbolt and move the AC compressor to get to the bottom bolt on the alternator.

 

I originally became concerned with the alternator when my wife came home from running errands and complained about the maxima's electrical system acting up (i.e. radio on and off, dash displays not working, etc.). The car was also running rough and after she got home and turned it off, the car would not immediately start again (no power). I waited about an hour before I checked under the hood, by then the car would start and I got the voltage readings I mentioned earlier.

Update: So this morning I go out to begin the process of removing the alternator (UGHH!). I decide to check voltage again across the battery terminals at idle and I get 14.1 volts. I measure directly across the alternator terminals and get 14.3. volts.

I take the car out for a 15 mile drive, running the ac at max, headlights on, rear defroster on, Bose stereo blasting, etc. and return for another measurement. At idle (with a/c, defroster, light, etc. still on) the voltage read 12.7 volts across the battery terminals. I turn off all the extra loads and voltage goes back to 14.1 at idle.

Obviously the alternator still works "good enough" most of the time, but I'm probably going to replace it anyway...

Thanks for the comments!