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2004 Nissan Sentra - is this problem really the alternator?

My alternator died a few months back, replaced it with a brand new one. Yesterday my brake light and battery light came on, which is what happened last time the alt went bad. On my way to a mechanic it completely lost engine power but not electrical. I had The gas peddle to the floor and it wouldn’t move but it was still running, all electrical still working and didn’t dim. Pulled into a parking lot, turned it off and tried restarting it and it wouldn’t even try to turn over but all electrical still worked normally. I turned it off and set for about 15 minutes waiting for help and then it started right back up and I was Able to drive about two miles normally before it did the same thing over again.

I got it to a mechanic and they tested the alternator and said it wasn’t charging. They replaced it and it ran fine last night but this morning my car would barely start and kept trying to die unless I gave it gas. I had to make a two hour trip home and the car did fine but the temp gauge never moved from cold. At first I thought the thermostat might have been stuck open but the heat worked. I’m confused by the whole chain of events and wonder why I never Lost electrical power and why I lost engine power if the alternator was the only problem. The car is starting fine now but I’m worried something else is about to go wrong.

I’m not sure about the alternator issue, but you might want to check your coolant level…I wonder if the temperature sensor is sitting in an air pocket. It can’t measure the temperature of air

If that was the sequence of events I would have to question the integrity of your battery… If it is internally damaged (read shorted) this will fry every new alternator you attach to it. Alternators are there to maintain the batt at full charge…they are not meant to bring a batt from discharge to full charge like a batt charger is supposed to do. Making the alt charge a batt is a great way to hurt an alternator.

So how old is your battery? Might be time to check its health…that’s the first thing I would be doing.

However if after re replacing the alt cured all the problems… then it could simply have been a faulty alternator the first time around…and you just experience the normal symptoms of such.

I’m sorry, I forgot to mention that is the first thing we did because we were thinking it was strange that the alternator would already be bad. So the battery is brand new.

Ok thats a good thing… Honestly it sounds as if you just had your first experience with a bad “new” part… Happens a lot, believe me.

Had something similar happen to me. Turned out to be a bad ground somewhere. Rather than trying to find the ground fault. The electrical specialist diagnosing the problem ran a jumper directly from the alternator to the negative terminal of the battery. Solved the problem. Was trying to figure it out for a month, several alternators and batteries before I took it to the specialist. Basically the alternator was not charging the battery due to ground fault and the engine was running off the battery till it drained down. Electricals still worked but not enough to keep engine running.

All this started after the battery was replaced? You could have gotten a defective battery.

There may be a bad connection between the battery and the alternator. To see if that is the case check the voltage drop between the two while the engine is running around 1500 RPM and there is a good load on the charging system. First measure the voltage between the output lead of the alternator and the positive battery post. Then check the voltage between the case of the alternator and the negative battery post. There should be less than .3 volts difference for both readings if the connection is good.

Suggest to ask your shop to do an alternator/battery test. A diy’er could just measure the battery voltage and get a good idea too. Before first start of the day the battery should measure about 12.6 volts. Then immediately after starting the engine, 13.5 to 15.5 volts. What do you get? Until you know for sure the battery and alternator are working correctly there’s no use worrying about dash lights and gauge problems. Those won’t work without a good electrical system.

The reason both the brake light and alternator warning light come on when only the alternator is broken is probably b/c the engineers at Nissan wanted to provide extra safety for the car owner in the event one of the dash bulbs burned out. If that happened at least one of the warning lights would come on and you’d know something was up and a shop visit was in order. My Corolla does that too.