Strange Electrical Problem

My wife has a 2000 Sentra GXE which has been showing some rather strange behavior for awhile and no mechanic has been able to figure it out. First, her check engine light has been going on and off for the past couple of years. Nissan techs don't understand the code the computer returns and they tell her not to worry about it (o2 sensors are in good order, according to Nissan).

Her car is running out of juice and we need to jump her battery every 5 - 10 miles. FYI, the battery is only two months old.

Right before the car dies, her lights will dim and the air bag light will begin to flash. We just had Nissan take a look at it and they said that both the battery and the altenator are fine and that the altenator belt was just lose. We pick it from the mechanic yesterday and it died again, this time is a not-so-friendly neighborhood.

We brought it back and they are going to swap out the altenator, but they are not sure that's going to fix the problem (they aren't 100% sure what the problem is). This sounds like a potentially expensive "test".

Anyone come across this issue before? Could it be anything other than the altenator? Could there be a short some where? Again, the car will charge fine, but the battery dies out after only about 10 miles or so.

Thanks

your right its not a cheap test to do, its what mechanics call "throwing parts" at a problem. any real mechanic would tell you this is the very last resort as far as fixing a problem. and it shouldnt even be necessary as far as a charging/battery problem is concerned. now its hard to diagnose a problem from a description i read over the internet, but it almost sounds like a bad battery or possibly bad positive battery cable, but i cant be sure.

that check engine light is probably emissions related, and i wouldnt worry about it, but id suggest you take it to another mechanic if they dont know what it means...that plus the alternator issue seems kind of retarted. regardless id start thinking about finding a new mechanic.

Regardless of the battery cables the alternator should still keep the engine running, it is when you shut the car off and try to start it again that the battery cables become an issue.

That aside... either the alternator is bad or there is a HUGE load somewhere that is sucking up all the juice that the engine needs to stay running, a multimeter and an amperage gauge should be all that is required to figure this out.

The flashing lights for the air bags are probably related to the voltage drop off, probably a warning that there is not enough voltage to make them operate if needed, I'm not positive on this though.

I too would recommend taking it to another mechanic, find a garage that specializes in Nissans, they have probably seen this before.