Has anyone else experienced the following problem: At night when my headlights are up, if I use the electric windows or the A/C comes on, or even if I put on the brakes, the headlights dim considerably for about one second. The DIC voltage display will drop from 14.0V (approx) to 11.6V when I run a window up or down. Then the voltage ramps right back up again. I know the alternator is supposed to ramp up and down electricity production so as to not kill the battery, but during this lag isn't the battery supposed to supply the extra current? I have never had this problem with a car, I have only ever seen it on my motorcycle with a mostly pooched battery. Does anyone have any suggestions?

This is a 2001 Z06, so if it is a mechanical or battery issue I want it fixed under warranty, but I have had GM check it three times now, and have gotten "it's within specifications" each time, even though the mechanic agreed that it is a very noticable drop. I had a cop question me about it at a ride-check (drinking&driving check) because I rolled the window down as I was pulling up. He thought I was flashing my headlights to warn oncoming cars. I showed him and he told me to get it fixed. Sigh. Thanks for any help!

imp.

 

I suggest you go to another dealer for the one your using its clear cannot find their butt with both hands.

Being the problem happens when you add additional current load I would suspect a bad cell in battery, a weak ground somewhere.

They should be able to do a load test and quickly find the problem and since it causes you to loose light level at night I would point out how very unsafe it is.
I'd contact G.M and make that clear.

 

I have experienced the same voltage drop... I plan to tell my dealer when I get the oil changed soon.

I'm getting my oil changed this weekend hopefully so I will Post my results and statement from the dealership. :eek:

 

I agree with Team ZR-1 that it is probably a bad cell in the battery. The Delco AGM battery in my 2001 coupe developed a bad cell after only three months. My advice is to get an Optima battery now and save yourself some headaches in the future.

 

Another tell-tale sign for a failing battery? :nonod::(

 

vette2001c5,
I am experiencing the same voltage drop under the same conditions. I already have the Optima Red Top.
Numerous C5's in our club have the same problem. Many tell me that its just a C5 thing and others tell me
to have it checked out by the dealer.
My car is a daily driver...not like the battery needs topping off. :flag
Matthew

 

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. This can point to a bad connector or cable. 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.

 

Thanks for all of the information! At the moment I'm leaning towards it being a battery issue, because it is only a momentary drop in voltage while the alternator ramps up, and it happens regardless of being at idle or WOT. That said, I have a friend here at work who replaced his alternator in his Oldsmobile every year for six years...

I think I will try switching batteries first, and if that doesn't fix it, I'll go try to fight with GM again about it. I'll post back with results.

imp.

 

If your battery or a cable/terminal was bad, you would notice your starter sounding "funny" when you try to start the car. If a battery cell was partially bad, there would be a time delay before the starter spins at full speed.

Many batteries are replaced for nothing.

 

Hmmm. I haven't noticed any strange sounds on startup... how much of a time delay would I be able to notice when starting if it were the latter case? My thought was to pull my truck battery and pop it in the car to see if it cleared up the problem, and if not I would haul in to GM again. Thanks again for your help!

imp.

 

A starter draws a ton of current from the battery through the battery cables. If anything is wrong in this chain, your starter will not sound like it normally does.