This only started about under a month ago. The dash lights - Brake and Battery - are on, or really, they flicker on/off and try to stay on when the revs rise. Typically when it's idling, the lights don't come on. Strange right. After I ran the car hard with high revs, the lights will pretty much stay on and not flicker until I restart the car again.

I checked the battery and it will do 12.5-12.7v with the engine off and 13.8 to about 14.9v with the engine and a/c on. I took it to O'Reilly and Autozone and they tested the battery and alternator, though it looks like the exact same testing tool, and they both said that the battery is no good while the alternator is good. But I had them test it like 2 months ago and the guy said that the battery and alternator were both fine. Could it be the alternator voltage regulators or diodes? I have an in-dash pioneer avic d3 with the vehicle dynamics display, though I don't know how reliable the readings could be, they seem accurate. The pioneer says that the voltage fluctuates between 13.8v and spikes 15.5v. Teh reading will be all over the place. ONly until I run the car hard, will the pioneer read the voltage as a steady 14.7v.

Whats up?

 

Your battery's dying. Get a new one before this one craps out completely.

 

K, I want to trust you...all you guys. I also tested my gf's civic and it reads 12.7v engine off and 12.7v-ish engine on, radio on, a/c on. So that is strange...but I think and know that every class of car is different like with comparing readings from trucks to econo cars.

But the car starts fine, headlights are fine, interior lights dont dim, or anything else that would seem like a dying battery. I don't want to really open up the battery caps to check water level. Also, fyi, the battery is about 3 yrs old and it is an original infiniti/nissan battery. I only have the pioneer navi headunit, 200w kicker amp and sub with stock speakers btw. Are my voltage readings way off?

 

I would just replace the battery. The cost of the battery might be worth the trouble. It's better than getting stranded some place without being able to get a jump. If you have a set of jumper cables, you should keep those in the trunk.

I had a car and the battery light would intermittently go on/off. The car ran fine, took it to get it checked out, and the dealer said it was fine. The alternator officially died a few days later. You can never really tell even after the tests say it's ok.

 

So, is the consensus really a bad battery? I'm also getting an odd shift from what I think is first gear to second. Like it "hiccups" almost, or hesitates or pauses a second goign into second - what was once never felt before. I would generally believe bluedream because of his post count - meaning that he's probably read and responded to alot of topics on this board....but it's really hard to know that is whats wrong.

 

Hell yeah trust your Texas brotha!!

Seriously though, that's the thing with batteries. They can get very squirrely when they start to age. The fact that your car seems to function best when you run it hard leads me to believe you have no alternator problems, it seems to be doing it's job. Your issues pop up when the car sits for a while and the battery is on its own and not being charged by the alt.

You can ride it out and see if the battery does fail if you want. You'll just have to deal with it when it does. Is your battery stock? You should really pop the tops and check the water levels though. If it's low that could also be causing an issue.

Hope this helps.

 

I honestly don't think it's the battery. You would definitely notice the trouble starting.

Once the car is on, the alternator takes over. The battery is just an afterthought because the battery's main mission in life is to start the car. When the engine is running, the alternator supplies the ENTIRE current for the car and is not meant to recharge the battery in any heavy capacity, but only to keep it at a maintained level. Having said that, you should see at least 13.5V at idle and NO MORE than about 16V or possibly a little less.

Overcharging may indicate the alternator is on the way out. The sensing circuit connected to the alt should aim for a steady voltage. If your voltage is jumping all over the place, you may have a diode trying to die.

 

UPDATE:

Ok, so it turned out to be the alternator. About 2 weeks ago I purchase a new battery and swapped it in and I had the same conditions so I returned it. My new Infiniti battery is only about 3 years old anyway. Now finally, the car was about dying and left me to run on battery alone! So I finally had time and money to get an alternator for it and POOF, the dash lights are gone and she runs beautifully. That noise is gone as well - I had a hunch it was the alternator will buildup on teh brushes. It all doesn't matter, as I'll be selling this car soon leading me to share my gfs car - an 03 civic.

Well, we're moving to Ithaca and we won't be needing two cars necessarily, and money is to come from selling my car. Oh well, that's life. If anybody is up in Ithaca, holler.

 

Hey, i know this is an old thread but ive had the same problem.
My alternator died before and i replaced it a few months ago. Then the lights came up again. I got the whole system tested and everything is charging fine but the lights are still there. So i changed the battery for the hell of it and they're still there. flashed the ecu and nothing.
I dont know what else to do. i dont want to change the alternator again. i just did that.
any ideas?

 

After much research and testing with a similar "battery- brake- light" issue, it turned out to be a loose ground at the battery post. Even just slightly loose causes the dash lights to come on sporadically.

Anyway, consider this if you are still diagnosing:
1. The EBrake wire gets grounded when off by default. So if it comes on along with the battery there is a good chance your entire system has a ground issue.
2. When the dash batt/brake lights are on monitor your voltage (for me it would drop from 13ish to 10 isn).

Note: my alternator and battery are less than two years old, so I had that knowledge (of course that is no guarantee)

Conclusion: If you have BOTH lights on there is an extremely good chance you have a bad ground somewhere in your system.

I also think if it were an alternator issue (like thought is was for a while), I probably would have had issues starting the car at some point. I also don't think a bad alt explains the brake light being on. Sooner or later a bad alt will allow your battery to drop below starting voltage. fyi.. I DO have an aftermarket alternator.

************UPDATE**************** Sorry folks I have to "man up" and eat my words as the Batt/Brake light still come on from time to time and I with the lights comes a nice voltage drop. I get the feeling its just a matter of time before I replace the alternator AGAIN! Good luck with you diagnosing.

Hope this helps some folks

 

was your alternator rebuilt or new? Rebuilds have been known to go bad prematurely or depending who rebuilt it

 

fail just saw this was an old thread...

 

rebuilt

 

I know its an old thread but i have the same issue for a long time and its driving me crazy. At first, brake and battery were only flashing a little bit but lately they stay on for more time. 1) I have UR pulleys. could it be? 2) i changed the alternator and battery (alternator is aftermarket and battery new just 1 month old so i dont think they r the problem. 3) i checked the belt (its good). I dont have electrical problems. everything seems fine. I was told a ground problem. They added a ground wire (6mm) and they told me to charge the battery a little bit and things will be fine. I hope so. Still trying to diagnose the problem.

 

Just because the battery is new doesnt mean it cant be bad. Have it load tested where you bought it, then have them charge it. I had a battery that tested good, then failed while charging.