Pauliescff

got the battery alternator warning message the other day. I had the alternator rebuilt about 2 years ago and the rebuilder mentioned that the alternator was on its way out. Can anyone check their voltages for me at the instrument cluster and at the battery?
1. Engine at idle-no accessories on
2. Engine idle-headlights and a/c on high
3. Engine at 2000rpm headlights and a/c on

thanks.

Plutoe

Do a proper load test or buy the girlfriend a hot dog!


PS: all should be near or over 14v

Pauliescff

ok. Thanks. Not sure about the hot dog. But ok

zzdragonz

checked the instrument panel using the onboard dyno diagnostics and got a steady 14.3V at idle.

Let me know if you solve this problem and what voltages are you getting?

use the dyno procedure:

1. turn key to one click after you set the dash to main odo menu.
2. quickly press the reset knob three times

you will get a voltage reading and you can turn on the car to get the voltage at idle.

let me know what your numbers are at idle, should be over 14V as some mentioned.

Pauliescff

So I was originally getting around 12 v at idle. I replaced the alternator with a rebuilt unit. At idle, with no accessories, I get 13.6 volts. With accessories on, it drops to around 12.9 volts. While driving, it will hold steady at 14.2 volts. When I put it in, the battery/alternator message went away for 2 days and came back. Any ideas? Does anyone know about an alternator fuse?

zzdragonz

at idle you should be getting 13.8 to 14.5 volts to be in the normal range. Not sure why you would get the same message after you replaced the alternator however...

anyone?

Pauliescff

sorry. With all accessories on, voltage drops to around. 12 volts

zzdragonz

sounds like you are not getting the appropriate voltage from your alternator
(constant 14V+), I will drive my car and see what the voltage is at and get back to you.

Pauliescff

Thank you. I've not had much success with rebuilt units from the major auto parts chains. I'm kind of thinking that this rebuilt unit is no good.

zzdragonz

Ok so I checked the voltage on both my 2007 c230 and ithey are nearly identical. 12.5v when the car is not on. 13.5v - 14.3v when driving. Rarely does it dip below 13.5 but maxes at 14.2 or 14.3v

What do these numbers mean for you? I'm not certain perhaps someone else can chime in.

Pauliescff

what voltage at idle with accessories on? A/c on maximum auto, headlights, rear defroster?

zzdragonz

It'll dip to 13.5-13.8 then slowily come back to 14.2-14.3v

Pauliescff

Thanks so much. Mine will dip below 12 volts and rise to maybe 12.5 volts.

zzdragonz

Hey Buddy,

I was able to diagnose my car this morning and it looks like it's doing it when cold out.

Here is what I did and how I alleviated the problem temporarily.

First, before starting the car I put it into dyno mode so I could monitor the voltage.

I started up the car and the voltage was at a mere 12V and would barely rise, say 12v - 12.3v. That's when I knew there was a problem, not entirely sure what yet. So upon noticing that the voltage was not climbing as expected I gave it a little bit of gas, around 1.5k rpm to warm it up, and the voltage started to climb slightly, but the red battery light did come on. I kept at warming up the car at 1.5k rpm and noticed the voltages started to climb, and before I knew it, the voltages finally came up to 14.2v

relieved by this i monitored it for a bit to ensure it would not drop back down.

I then took out the key, set it to dyno mode again and started the car.

The red battery light was gone and I was able to drive it without worrying.

So, in conclusion what I would do is follow those steps I mentioned and see if your voltage does come back to normal 13.5-14+v When it does you have to take out the key to clear the code.

For my particular issue, I'm not sure if it's the battery or the alternator that's starting to have problems, the old owner mentioned that the battery was changed out 16months ago, but I did notice some white corrosion around the neg. terminal.

Hopefully this problem gets solved rather quickly, and hope this helps you or anyone else in the future.

Let me know what you find, cheers.

mtnman82

Here's what I see on my '03 c230k, 108K+ miles, battery replaced ~3-4 years ago by MB (called them from a hotel when I was out of town and they came to replace in the parking lot for<$150), original alternator:

Key On Engine Off I see ~12.5v. When I start it the voltage slowly rises to 13.3-13.4v. The second I start to drive it's up at 14.3-14.4v. With the A/C on it will dip to 13.6-13.8. If I turn the car off and start it back up again I see the same behavior. If I rev it up past 3000rpm the voltage goes up to 14.3-14.4v but comes back down to 13.3-13.4 when I go back down to idle. I also notice the lights dim when at idle in the dark. I'm thinking the alternator should be replaced somewhere along the line here, due to mileage on the car and reading about other's woes here on the forum...

D. Strauss

Car idles rough! Wondering if I have a bad alternator? Electrical test showed good battery but failed voltage regulator(below 13.6). If this sounds accurate can the voltage regulator be replaced while the alternator remains on the vehicle?

dboyrusky

Sounds normal, that about what i get as well. I think its normal.

dboyrusky

Car off 12.3 - 12.5
Car idle 13.7 - 13.9
Accelerate 14.1 - 14.3