sd2734

OK guys here is the deal:

'01 Sentra GXE 75k miles. My "Check Engine" light stays on with P0420 (O2 sensor problem) which sensor I haven't replaced yet.
But the problem is different.
While I was driving the "Battery" and "Brake" lights came on and very soon the "Air Bag" light also lit. There was no noticeable change in performance till I got home. The next day I couldn't start the car (even the doom light didn't come on). I measured 3.5 Volts in that 2 yrs old battery and jumped with cables. The car started just fine and afetr 5 minutes the voltage went to 14.3 Volts. I decided that since the alternator is charging the problem is with the battery and since it was under warranty I replaced the battery with a brand new one. On the next day following the replacement, the car couldn't start again and the voltage fell down to around 6 Volts!!!! I double checked doom light, trunk light, headlights etc. for a source of potential power drainage, but nothing was on--some mysterious source had drained a brand new battery. Crazy!!! I don't even know what to look for as a potential problem. Any suggestions?
Thanks.

 

b15chik

i said this in your other thread on b15, but yeah it sounds like something with the alternator. maybe a wire is corroded or loose or the alternator just took a crap

sd2734

Thanx,
I measured with a voltmeter and it read 14.3 volts--it seems to me that the alternator is charging. However, the next day the battery was almost completely discharged WITHOUT the car running, therefore isolating the alternator. Is it possible to be a relay or ECU. Do they have back up batteries that might have died? I checked all light for possible open and still could not find anything powered on?
Any more suggestions?

ralph1902

Having exact same problem you described in your message below except on a 98 Sentra GXE with 104K. I was wondering if you were able to fine the source of the problem...

Would appreciate any clues as to the problem.

Thaanks!

sd2734

Hi Ralph1902,

Sorry for the late reply, but I seldom check this email account.
Hope this message getes to you before you disassemble the entire car or taken it to a mechanic!
I recharged the battery, with the engine running, and then disconnected the alternator cables (to isolate the alternator from the charging system) and the battery did not drain overnight. Then, I figured that it was safe to assume that it was the alternator and replaced. Never had this problem again.
At the electrical shop I was told that I diode in some instances can cause this problem and the guy used a bench test to confirm that the alty was bad.
Hope this helps!
Regards,

 

ralph1902

Thanks!

Ralph

Doja

take it to sears free diag on alternators. They try to sell batteries of course, and with that comes electrical system checks. they call it a Die Hard service. Anyway, if you want to do it at home and check for parasitic draw on the battery, all you need is a digital amp meter,
or DMM or DVOM whatever. With the vehicle off. Disconnect the negative terminal, bridge the neg terminal and neg post with your meter set to amps. If the meter reads over .015 you probably have something drawing batttery power. In this case I usually check for a new stereo install or car alarm. But it can also be a faulty module too shorted to ground.
Thats when I start unplugging stuff until the amp draw stops. This is not very easy to properly diagnose, if you dont know a lot about your car, or electrical circuits your best bet is to take it to a mechanic. Hope this helps, you should get the alt diodes checked first
because even though your voltage shows good it might not be a good alt. I think even walmart can check it for free. good luck