Got a puzzle for c4c5...it's probably a simple one for you.

[97moneypit]

Not sure how to explain this odd thing I noticed yesterday and again this evening. I have only noticed it when the lights are on.

I have a '97. I left work, went to a bar, had a scotch and now I am seeing things.

When I got to the house, and this happened last night too...(not the scotch) I noticed that, with the car running, whenever I stepped on the brake all of the lights including all interior lights would dim as I depressed the brake pedal.

So I experimented and turn off the engine. Stepping on the brakes did not cause the lights to dim without the engine running. The main difference it seems is that the power brakes are no longer active with the engine shut off.

Any ideas..or do you need some more information?

It seemed that last night, the lights would dim without activating the brakes, almost as if some electrical device was kicking in intermittantly....

I still need to do some more experiments to find out the extent of this little quirk.

 

[c4c5specialist]

HI there,
Ok, your right, interesting puzzle.
A few questions here, please.
Have you ever had your DIC voltage level recalibrated by a dealer with a Tech 2?????I ask this, only to make sure you are getting correct readings, it will not affect alternator output, just give you the correct readings.
With your DIC on Battery VOLTS, check the voltage before the lights on, and then when you turn the lights on. The voltage will drop momentarily, and then recover, and go back to where it was before the lights turn on.
Have you noticed if your battery seems to be turning over the car a little slower than normal???????
When you have the lights on, then you press the brakes, check the voltage again, before and after, do you see the voltage drop for a minute, and then recover to the correct level.
Please note, you may see at least a 1.5 volt drop, and sometimes more, however, it should recover within 30 seconds, to the operating level, of 14.2-14.8.
Please keep us posted, c4c5

 

[O'boy]

I don't want to intrude on the discussion, but my C5 blinks all the time. You don't need to apply the brakes - just driving down the road everything dims slightly then brightens again. This happens every 5 - 10 minutes.

 

[97moneypit]

O,boy,

I noticed the same thing today. It seems to flicker more so when it was idling. It seemed to stop once I got up to highway speed. But here's my take on that....either

1. I am driving too fast to comfortably take my eyes off the road long enough to really observe the flickering... or

2. It mat be flashing so fast that it's not perceivable....

Could it be related to ignition impulses? I am about to go try the tests that c4c5 mentioned. Maybe with a little more info I can narrow this thing down.

 

[02 C-5]

I have an 02 with the same thing , it will dim as I am driving at steady speeds and dim if I step on the brakes . I think it is dimming while driving because of the A/C . It will dim for a second and come right back . I do not think there is anything wrong , it just noticable . The real question is why does it dim so much or why does the voltage drop so much ? I have not seen anything wrong with my DIC either , it might drop 1 volt .
Thanks ,
Joe

 

[97moneypit]

HI there,
Ok, your right, interesting puzzle.
A few questions here, please.
Have you ever had your DIC voltage level recalibrated by a dealer with a Tech 2?????I ask this, only to make sure you are getting correct readings, it will not affect alternator output, just give you the correct readings.
With your DIC on Battery VOLTS, check the voltage before the lights on, and then when you turn the lights on. The voltage will drop momentarily, and then recover, and go back to where it was before the lights turn on.
Have you noticed if your battery seems to be turning over the car a little slower than normal???????
When you have the lights on, then you press the brakes, check the voltage again, before and after, do you see the voltage drop for a minute, and then recover to the correct level.
Please note, you may see at least a 1.5 volt drop, and sometimes more, however, it should recover within 30 seconds, to the operating level, of 14.2-14.8.

Please keep us posted, c4c5

I do not know if it was recalibrated before I got the car. I have not had it recalibrated.

With the car running, the DIC voltage readout jumps between 13.3 and 13.4 typically. Sometimes between 13.2 and 13.3. When I turn on the lights it will drop. The dropped ranged from the lowest of 12.9 to about 13.2 and anywhere in between.

It seems to crank the engine just fine. There doesn't seem to be any difference from a few weeks ago.

I get the same drop in voltage. THe lowest has been to about 12.5 with the brakes and lights on.

The DIC is showing an operating level at around 13.3 to 13.5.
Should it be showing 14.2 to 14.8. The owners manual doesn't really say other than that you should see a readout similar to 13.5. It doesn't actually say that that is the correct operating level.

Read my post above to O,boy. I also noticed that it's not as bad initially after starting the car. THe flashing increases in intensity later on as I drive it more.

Do you think maybe putting in a fresh new battery might be a good starting point?

Thanks

 

[c4c5specialist]

Hi there,
Ok, well, first, yes, your DIC will need to be calibrated, for the correct voltage signal. What it basically needs, is an actual multimeter, measuring voltage output at the terminal at the alternator, and a Tech 2.
So, when you are monitoring output, you program in the correct reading.
I can tell you, you can do it on any c5, and it works, just to give you a correct reading.
Do you have a problem??? Well, honestly, I dont think so. As other members have noted, it does happen on all c5, to an extent.
The actual function of the alternator is PCM controlled, so it has to see the voltage drop first, and THEN increase its output to compensate. This is the main reason you see the dimmin, and then it comes back.
I hope this helps, c4c5

 

[lrrp 51]

I have the same problem with my 98. Every time there is an increase in the electrical load, the lights dim for about 1/2 second. All of the blue lights on the IP flicker at idle.

I think that the periodic dimming others have mentioned is due to the air pump cycling. At least it is on mine.

The DIC reads about 1 volt lower than a meter across the battery terminals. Voltmeter gives 12.5v key off and 14.5 running.

The DIC display fluctuates rapidly between 12.5-13.7 and dips into the 10's when the air pump cycles and the lights dim.

Now, to muddy things up a bit, the other night on the way home from work, the DIC was glued at 13.4, no dimming, no flickering so I know it can work. However, after a restart on the same trip, it went back to dim/flicker.

I get low voltage warnings, lose the Key fob synch overnight and the DIC reinitializes after a start. I haven't checked cranking voltage but it must get low to reinit the DIC.

I don't know if it's related but most of the time the headlight doors won't open with the engine running. Engine off they're fine.

Lots of symptoms of a weak battery. But is the battery weak on it's own or because of some charging system gremlins?

 

[Ralph Kramden]

The actual function of the alternator is PCM controlled, so it has to see the voltage drop first, and THEN increase its output to compensate. This is the main reason you see the dimmin, and then it comes back.

I guess this means that the PCM is functioning as the voltage regulator instead of the old style incorporated-into-the-alternator regulators?

Is this something that GM is doing in all of their cars now?

Does this mean that the C5 alternators no longer have built-in regulators?

Seems like a step backwards to me, if this annoying side-affect is now common in GM cars.

 

[c4c5specialist]

I guess this means that the PCM is functioning as the voltage regulator instead of the old style incorporated-into-the-alternator regulators?
Actually, no, as the regulator is still inside the alternator, but it is dependant on the PCM input, to function at a given output.

Is this something that GM is doing in all of their cars now?
Yes, due to the fact that when you reduce your alternator output, you reduce load on the engine, which helps with EPA fuel mileage guidelines.

Does this mean that the C5 alternators no longer have built-in regulators?
See above.

Seems like a step backwards to me, if this annoying side-affect is now common in GM cars.

Allthebest, c4c5

 

[AZMike]

I ditched the crap AC Delco battery and put in a Red top Optima I got at Costco. All of my strage flickering and DIC charge system faults have suddenly gone away.

I also noticed that the stock battery on the car is only 500 amps or so. This is truly pathetic for a car with so many electrical accesories on it. The Optima has over 700, and it seems to have cured a lot of the problems. My stereo amp doesn't suddenly shut down anymore as the volts are not dropping down to 10 like before.

The car even starts much faster when it's cold too.

Most auto manufacturers put in the cheapest battery they can get their hands on. In fact, most batteries under 550 CCA's go for about $30. That should tell you how much GM invested in the battery!

 

[cavettefan]

AZMike,

Actually, less than $30, because GM buys in bulk. Maybe more like $10 - $15 is GM's cost.

 

[lrrp 51]

Well, to make a long story short, if you have a just-barely-snug negative battery cable terminal you may experience:

Headlights dimming when you apply the brakes.
IP and radio displays flickering.
Reinitialized DIC after a start.
Low voltage warnings.
Loss of key fob synch overnight.
Rapid fluctuations in the DIC voltage display.
Headlight door opening problems.

All of the above was fixed with one twist of a wrench.

You won't pick it up with a DVOM so before you run off to the battery store, check your terminals.