I have a 2006 Nissan 350z enthusiast Auto with 129K Miles. One afternoon I was going to pick my daughter from school and the car won't start at all. No clicking and no engine rev, just complete dead. I did a battery test with my multimeter and battery is giving me 12.6 volts. Then later in the evening, I wanted to do more testing, I turn on the headlights which it did but I hear this fading sound as if the power is draining out of my car. Then I put the key in ignition, and I see lights on my dashboard. I turn the key and the car doesn't start.

Now I'm trying to figure out what's happening? After this, I tried to turn back my headlights on, but it didn't work, no power at all. After an hour, I tried to do the same thing, the headlights went on, tried to turn the key in the ignition and died again. Please help me fix or what could be possibly wrong with the car.

Thanks alot

 

Multimeter test... 12.6v. That's decent but... a stack of D-cell batteries can show you a 12.6v output. Under load (like trying to start), that 12.6v will draw down to nothing with insufficient CURRENT (amperage) to do anything.

Basics first:

How old is the battery? Does it start with a jump?

If a jump doesn't do it, check your terminals and battery posts. They might need a simple cleaning with a battery brush. While cleaning that, also disconnect the negative ground on the fender wall and clean/sand both the cable end AND the ground point on the car. A bad ground can easily kill starting and power to any accessories (like headlights). (Or, in my case, the cable itself fell apart from the inside corroding, with no outwardly visible signs of impending failure)

If there's no improvement then it's likely your battery is toast. But the key here is that it's an insufficient power issue.

If yes, it starts with jump, look at your gauges, is it showing excess charging? (>15); let it charge for a while then take car to a shop to have them load test the charging system/battery. That simple test will pinpoint which component is to blame... alternator/regulator, battery, etc.

Once you've got that portion of the equation repaired/replaced, then you can start looking for other issues beyond the basic electrical.

 

This^^^

It still surprises me when starting problems arise and the post doesn't include any details of how old the battery is. Our lead acid batteries have a useful life of 3-4 years; anything over that is a bonus. Cleaning the terminals and checking for a solid ground (as Mic suggests) is another basic step that should be taken to ensure a solid power supply. Hate to say it, but our Z33s are getting older and rely on a electrical system that degrades no matter how reliable it's been.

 

Battery is about 4months old, I just did the cleaning and ground test and all seems to be ok. Jump start doesn't help either as its doing the same thing.

 

I'm not so educated when it comes to cars, main reason I seek help from the forums is to save money and do as much repairs as possible myself. Something weird and surprising, I talked to this guy who previously helped me replace my starter and made an appointment on Friday. I wanted to make sure that my starter isn't the problem here coz he warned me about installing refurbished parts (at that point I had no choice as it was the cheaper option).

Decided to test the starter using jumping cable from the fuse box. I read the manual and took out the relay and R4 and used a jumper cable to start but nothing happened, car's still dead. I put everything back together and wanted to give another try, but this time the car actually started. I waited for few minutes thinking that the car will stop but something fixed by me removing the relay and putting it back. Is it possible that the relay is going bad?

Thanks