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Electical Troubles with My Nissan Sentra

I’ve been having a bit of a problem with my 99 Nissan Sentra that is becoming more and more costly every day. It started with my airbag light flashing, so I pulled over to see what might be wrong. I turned the car off, and when I went to start it again it wouldn’t start. I had the battery checked out and it was fine; I ended up changing the starter and the ignition switch. This worked for a week. Later I left my car running in the morning to warm it up, and it did the same thing, the airbag light came on and the battery went dead. I jumped it and the battery wore itself out again, so this time I took it to the mechanic to replace the alternator. This worked for a week. This time my wife was driving down the highway, the airbag light came on again, and the battery went dead. After a costly tow from the police impound to my home, it will jump, but the battery slowly dies. I would love some advice before I end up taking it back to the mechanic again. The only noticeable problems the car has (aside from the obvious battery going dead) is that there is a belt that squeals when I have the air conditioner turned on and I have an oil leak somewhere. Someone help me before I waste any more money! My best guess is that someone has put a voodoo curse on my vehicle.

If you know how to use a multimeter (cheap sub $10 at harbor freight), measure the voltage across the battery with the engine running. It should be 14.5-ish volts or so.
I bet you have a bad connection from the battery to the frame, engine or alternator. The squealing could be a cause as well, if that belt drives the alternator.

I’ve had this exact same problem with my wife’s car two times about two years apart. Your oil leak is frying the voltage regulator inside your alternator. When your battery voltage drops below 10 the motor can’t run right and the airbag light is used to flash the error code. The oil leak is very common on this model car and is coming from your front main seal, timing chain cover, or valve cover gasket. Fix the oil leak, replace the alternator, replace both belts and top radiator hose because they are oil soaked and should explode soon. I guarantee 99% chance your problem is one of these.