Mechanics

ALTERNATOR PULLING 0.5A ALL THE TIME

1997 Nissan Maxima

Electrical problem
1997 Nissan Maxima 6 cyl Two Wheel Drive Manual 186000 miles

My problem started as a battery that went dead when my car sat for 2 days. It went dead on its own - no lights left on etc. I traced the problem to the alternator pulling 0.5A all the time. I verified the drain was coming through the field supply by pulling the fuse for the field - when I did the drain went to 60 mA. I bought a new alternator and put it in. It charges when the engine is running (14.1V at idle), but the drain was still there. I took it back and got another new alternator. The drain is still there. I can hear a very slight humming (about 200 Hz) coming from the alternator when the field fuse is in. When I remove the fuse, the humming stops and the drain goes to 60 mA. If I remove the B+ wire from the lug bolt on the alternator the humming also stops. I'm stumped. I can't believe I have received 2 new alternators that were both bad. The problem is clearly current flowing through the field winding. I tried connecting a new ground from the alternator case to the battery - that didn't stop the drain or the humming. I'm stumped. Any ideas?
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Studioj
May 17, 2009.



Hi studioj,

Thank you for the donation.

The problem is from the alternator and though hard to believe, new or rebuilt alternators do fail out of the box. There could be a design flaw resulting in the likelyhood of similar problems from similar alternators. My personal record is 3 faulty rebuilts at one go.

Were the purchased alternators used, rebuilt or new?

Did you try unplugging the 2 wire connector from the alternator? Was there any voltage from the Yellow/Red wire?

KHLow2008
May 18, 2009.
Here is the history on the alternators. I'm really skeptical that I have a bad one. The odds would have to favor me winning the lottery for this thing to be bad.

1) OE alternator replaced under recall by Nissan at 120K miles
2) Battery started draining at 180K miles and replaced with a brand new alternator. The drain continued
3) New alternator replaced with a rebuilt alternator. The drain continued.
4) 3rd alternator replaced with a rebuilt alternator. The drain continued and now I notice the humming sound when the battery is connected and the key is OFF.

One other thing I neglected to mention. The battery light in the dash never comes on so I am inclined to think that the bulb is open. There is supposed to be a bypass resistor but is it possible that this is a contributing factor.

Tiny
Studioj
May 18, 2009.
The charging circuit is rather simple and does not show any bypass resistor.


http://www.2carpros.com/forum/automotive_pictures/192750_ChargingCircuit97Altima_1.jpg



Since there was a recall on the alternator, I would not discount the possibility of bad alternators. The possibility of more than one bad alternator is there.

The buzzing indicates power is being passed through the alternator IC regulator and that should be the main culprit.

If you look at the circuit diagram, the system is different from most other cars which uses ignition switch power for the S terminal ( white) wire. Maybe you can consider changing the power source for this particular wire to operate only with ignition switch at ON and START.

KHLow2008
May 18, 2009.
Interesting. I have not had the dash apart (at least that part of it) but my Haynes manual shows a resistor in parallel with the bulb. I had thought about your suggestion as a simple solution to the problem. It seems odd to me that the mfg would not apply power to the regulator IC only in the key on or start position anyway. That may be the route I take. I had wanted to leave everything stock but I'm coming to the conclusion that the way the factory did it may have been just plain poor design. What really bugs me is that my original alternator was working fine before the recall fix! Thanks for the suggestion.

Tiny
Studioj
May 18, 2009.
Just noticed that your diagram is for the Altima. Can you verify that the charge circuit is the same for the 97 maxima?

Tiny
Studioj
May 18, 2009.
Sorry for the error.
There are differences in the circuit and the resistor is across the charge indicator bulb.

Unless the IC regulator is bad, otherwise the resistor should not be the cause of the problem.


http://www.2carpros.com/forum/automotive_pictures/192750_ChargingCircuit97Maxima_1.jpg


KHLow2008
May 19, 2009.
After ripping the dash apart and finding both the bulb and the resistor in the indicator circuit to be in good condition (it's a 100 ohm resistor BTW), and then tracing the circuit back to the alternator plug and verifying that if the wire on the indicator finds a path to ground the indicator light does indeed illuminate, I've concluded that yes, the regulator in the 3rd new alternator is bad. Since it takes about 2 hours to pull the alternator and since no shop will test the regulator before giving me another one and since I've had 3 bad ones in a row, I've decided instead to re-route the field wire on the alternator to a B+ position that is only on when the key is on. I don't know why they did not do this in the first place - makes a lot more sense than leaving the field energized all the time.

Tiny
Studioj
May 21, 2009.
You have equalled my record for 3 bad alternators in a row. Lol. Sometimes things have to be done the hard way.

Guess we have resolved the manufacturer's poor design. Maybe we should apply to the mfg for royalties for helping them solve the problem. Lol.

The recall should have been for the same problem. Though it was working fine then but there was a possibility it could fail anytime. Problem was the recall did not fix the problem as the design was flawed.

Glad to be of service.

KHLow2008
May 21, 2009.
I suspect that what has happened with regard to the recall is that the remanufactured alternators are not getting new regulators and are being put back out on the market with the old regulator design that was faulty. I'm pretty sure the dealers - who were doing the recall work - would put brand new parts in or at least parts they knew were not going to result in a call-back but the reman units going to the auto parts stores for the shade tree mechanics appear to still have at least some with faulty regulators in them.

Tiny
Studioj
May 21, 2009.
You have a point there. So anybody who goes for the reman would have to ride their luck.

But then the recalled alternator failed for you. Was it the same problem? If not you could have replaved the carbons and have a better alternator than the remans.

KHLow2008
May 22, 2009.