I noticed the other night that my head lights would dim when I pushed the brake. Also, noted the lights (low beam only) would really dim when I pushed the window buttons. Checked the DIC voltage and it said 13.9 but would fall back to 12+ (something) under a load, like the window button. BTW, my dealer replaced the alternator several months ago.

This morning I fired up the DIC (before starting the engine) and the battery voltage was reading a wimpy 11.5 volts. As soon as fired up the engine the DIC went up to 14.2 that tells me the alternator is at least trying to do its thing. While the engine was running with the lights on, I pushed the UP window button and the DIC dropped from 14.2 to 12.2 volts.

I wonder if I have a weak sister AGM battery.

Dick

 

Dick,

I just got my car back from the dealer yesterday for the same problem. I got my engine rebuilt during the month of Oct. and after I picked it up (the dealer had everything apart in the engine compartment) I had and electrical problem similar to yours.

Do the LED's on the clock and HVAC flicker also?

I suggested to the dealer that there was a ground wire that was left off. They came back and said it was a corroded wire (they just removed everything and then put it back..corroded my butt)

They id'd the ground terminal as: A102 Cicuit 150 if that helps.

The important thing is that what ever they id do...it's fixed.

When I was talking with the mechanic he was looking at a ground terminal in the front of the engine bay, drivers side that was close to the headlight.

good luck, I would start there.


[Modified by Gary2KC5, 9:24 AM 11/3/2001]

 

> They id'd the ground terminal as: A102 Cicuit 150 if that helps.

Sorry that means nothing to me. I have not idea where to look

>The important thing is that what ever they id do...it's fixed.
>
>When I was talking with the mechanic he was looking at a
>ground terminal in the front of the engine bay, drivers side
>that was close to the headlight.

I'll tak a good look in that area this morning after the car's bath

No flicker in the DIC....some of the dash lights dim under a big load
like the window button.

Sure would like to know what reading others get on the DIC after the car
has sat overnight. My understanding was a 12 volt batter should always
be above 12 volts...like 12.5 and anything under means is is nearing death.

After being zapped by the alternaterm mine comes back to 12 volts.

Dick

 

I just checked again tonight and even after being charged with the alternator, the
voltage is down to 11.5 volts before starting the car and it goes up slowly to 13.5 to
13.9. The low beam light still dim when i use the UP window control. I also have
noticed the green dash 'MPH' liight also dims.

I did not see any ground wires to check under the hood. Maybe someone can provide
a better clue to finding ground connections that need to be checked.

Dick

 

Here is the answer I gave on another low battery post a while back. Please disregard any info not pertinant. If you did a search through the archives, you will find numerous threads on the subject.

There are so many things that can cause this symptom that it is difficult to remote diagnose the problem. Many times there is nothing wrong, but you can check things out before going to the dealer.

My own FRC's lights will dim when the head lights are on, AC full blast and stopping at a stop sign. There is nothing wrong with my system. The standard GM alternator does not generate a lot of current at idle. It will take two people to do all the needed tests. One will need to blip the throttle.

Unfortunately you will need both a DVM AND a clamp on DC ammeter to fully diagnose the problem. A DVM cannot tell if your alternator has low current output. You need to measure all voltage drops across all the cables in the charging path. You also need to measure how the charging current divides between the engine, battery and the accessories. Attached is a standard blurb I gve people about the GM alternator.

The standard 105 amp GM alternator is a POS. It has a partial failure mode that fools most mechanics into thinking you have a battery problem. It even fools most of the new automatic battery/alternator diagnostic testers that the techs use. I just put my 3rd alternator in my C2500 with 45k miles. I had to argue many times with the techs who tested my truck and said it was my battery. The failure mode is that the alternator cannot put out full amperage anymore. It will put out > 13 volts though, fooling you into thinking it is OK. The engine, accessories and DRL's in most GM cars draw a ton of current. If the alternator is only putting out say 50 amps, then it starves some of the systems or the battery for power. The car will run and start, but over time the battery will go dead and some systems will operate irratically.

The only real way to test the charging system is to use a DVM and a DC clamp on current probe. Measure the total amperage coming out of the alternator and then see how it splits between the various systems and the battery. A bad alternator will put out say 40 to 60 amps and only 2 to 5 amps will be left over to charge the battery. You also need to measure voltage drops across wires to make sure you don't have a bad terminal on a cable or a bad ground.

If your battery has ever gone dead, you jump the car, and then run it without fully charging the battery, your alternator will overheat and have a shortened life. The alternator also will have a shortened life if you use the AC and lights a lot. Also large aftermarket stereos will also overheat the alternator.