Today I noticed my battery light would turn on and off intermediately. It will eventually turn off completely. I have replaced the battery and alternator about 5 months ago.
Any idea what i can check?
This has happened every time I started the car today but it will turn off after a few minutes

 

Probably be a good idea to connect a digital voltmeter across the battery.
Should read around 11.8 - 12.5 volts off, 13.8 - 14.5 running.

 

Check for tightness of cables and grounds.

 

The wiring diagrams for our cars are not completely accurate or detailed.

But the theory of how that light works is this:

• One side of the "light" goes to switched ignition 12 volts. The other side goes to the tertiary winding in the Alternator thru a diode. As long as the alternator is healthy and spinning, that winding should have MORE than 12 volts on it, and the diode prevents "reverse current" which would light the light. Now, if that winding is well below 12 volts, the light, thru the diode, sees a 'ground' and lights. This indicates that the alternator is simply not charging.

• The microcontroller in the instrument panel is also capable of providing a "ground" or "low" to the light. Exactly what that microcontroller 'sees' to cause it to light the light is not well documented. I would suppose that the controller is watching, that is, comparing, 12 volt lines in various places so that it can determine if system voltage is low in places even tho the alternator is doing it's job - this leads to 100/80's suggestion of checking battery posts for corrosion and tight, good connections; ground connections, etc.

A fundamental check is Ala_Xfire's suggestion to look at battery voltage with the engine either idling or revved up to, say, 1000-1200 rpm. At those times, I'd be disturbed to see less than 13.5 to 13.8 at idle and I'd expect to see 14.0 or more at 1200 rpm. Not seeing these voltages would, to me, implicate the alternator, most likely.



If this gets REALLY involved, keep in mind there is a chassis-to-engine block ground jumper under the car, if this gets loose, corroded, etc., the car SHOULD have a hard time spinning the starter, but it may actually start - but the charging of the battery by the alternator would be weak at best. ONE GUY on Facebook found this to be the issue in a similar situation. But that's one guy in the seven years I've owned one of these cars.

 

Mark, the next time I am under the car with pan off, I want to check this ground cable. Can you give me an idea where it is located? From what to what? It is hard to understand that a ground cable does not go to the engine first, then to the body. I think when I get time, I am going to run a ground cable from the battery to the engine block for better measures.

James

 

I don't know where it is. But I actually DID the mod to my Graphite about a year before it was lost. I grounded the small cable to the chassis (where the factory cable fastened) and the heavy cable went to the block. I THINK I used the alternator mounting bolt, but I just cant remember.

Again, I never found the block to chassis jumper, but I know one guy on Facebook DID when his corroded in two!

 

Mark, the alternator mounting area is exactly what I was thinking -easiest. BUT most OEM ground cables go directly to a bolt that fastens to the block itself - just something I noticed over the years.

James

 

Yea, I know. I just can't remember what I did, never snapped a picture, and the car is gone.........

 

On my car there is only one ground cable and it goes to a bolt on the chassis 3" from the battery.
I tend to think the '04 ground had two cables, a large and a small one. Could be wrong though.
I think there is a ground from the transmission to the chassis, again I could be wrong on that as well.

 

My 2004 only has one cable attached to battery ground to fender:

 

My 2008 has the same single 'short' wire from the Neg post right to the P/S inner fender well. Nice to see that 'stud' with a nut on it, seems a good place to attach a #6 wire terminal lug routed to the engine block at some point of access. Same as replacing the whole cable, and it would do the same thing?


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Yup, my Graphite was the same way. I used the cable I showed you, attached the smaller wire to the stud in your picture and ran the heavy one to the block - the way we did it for HOW many YEARS?

GG, I prefer my way, as the stamped terminal/cable connection is more resistant to corrosion than a lug under the ground bolt at the chassis.

 

Yeah PG, six of one, half a dozen of the other (some will recognize that comment), whenever I use a terminal lug in a vehicle, I solder after crimping to prevent water absorption. After that I seal with a very good grade of electrical tape. Know all too well corrosion finds its way into crimp only connections. Just as good your way of course!


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