Low voltage at idle

[Eric91Z]

Well, I have a new "thing" that has popped up on the car. I was coming to work today and had gotten on it a couple times to get around cars/semis on the interstate. I got off at my exit and sitting at the light I noticed the instrument panel lights were a little dim. So, I looked down at the volt gauge and it is showing 12 volts.

Watched the radio display and it was alternating dim to light. Car was idling smoothly and right about 600 rpm where it always does in drive. Put it in neutral and the rpms came up just a little and volts showed about 13. Gave it a little gas to about 1000-1200 rpm and volts back up around 14 where it is normally at.

Got to work parking lot, turned car off. Started car back up and sitting at 14 volts at idle in park, and about 13 volts at idle in drive. Not sure if the alternator got a little heated up while getting on it or what. I have not checked since I got to work this morning, but will be watching closely on the drive home tonight. Especially since it will be dark by the time I am on the road and will have light on, radio on, etc.

Earlier this morning I had lights, radio, heat seater, and rear defroster on with no problems showing. Not sure if my alternator is dying or what. Any ideas or input? I am taking the car in Saturday morning for an oil change, but not sure if they will have the time on a Saturday to check the alternator/charging system.

[fastblackmerc]

Still under warranty? Bring it to the dealership for a checkout.

[SergntMac]

Normal behavior. Not a normal condition, just bahavior to be expected with all that you have turned on at that moment.

If you have tune going on, the tuner can adust your idle in gear setting, 600 RPM might be a tad low with all that load on it. There's also a set screw on the throttle body linkage that may help you through the winter.

[TripleTransAm]

I see the same thing, sometimes. With lots of things going on, I can see a healthy 14 volts while stuck in traffic, then much later on, the same situation results in 12 volts and dim lights/slow blower/etc... sometimes even with LESS accessories running. Either something is wrong with the alternator (heat related, as you put it) or the PCM has decided to lower the charging output for some reason only it knows (for now). Since the PCM controls the amount of charging, that would mean some set of criteria were met to get the alternator charging less.

For now I'm not too worried about it (except for the annoyance of the slow blower when I desperately need it on a foggy-window day in stop/go traffic)... my MM#2 appears to have had a replacement Ford battery installed at some point (as did my MM#1, after 9 months) so I think I'm okay for now.

I'd doubt it was heat-related, since the last time I noticed this I am fairly sure I had NOT honked on the car all that heavily that morning (in fact, I might have let it idle in the driveway a bit longer while I cleared some heavy wet snow off of it).

And I too have seen the behaviour of shutting the car off and immediately restarting to find the slow idle voltage to be much higher than on shutdown. Go figure.

[Blackened300a]

I only noticed this issue since I installed the U/D pullies, Before that it was a steady 14v with the stock idle setting.

[Eric91Z]

I see the same thing, sometimes. With lots of things going on, I can see a healthy 14 volts while stuck in traffic, then much later on, the same situation results in 12 volts and dim lights/slow blower/etc... sometimes even with LESS accessories running. Either something is wrong with the alternator (heat related, as you put it) or the PCM has decided to lower the charging output for some reason only it knows (for now). Since the PCM controls the amount of charging, that would mean some set of criteria were met to get the alternator charging less.


This is what I had this morning. Lots of stuff on and working normally. Then when I got off the interstate I just had the radio, lights, and heat going, but the cooling fan was running (which is kind of funny, too. I have had that a few times this winter when it is 25 degrees or below and the cooling fans are running after being on the interstate for a while). So, I guess I will see how it behaves when I leave work and drive home now.

Will report when I get home how it does. And, yes, the car is still under warranty with only 15,300 miles on it and 1.5 years since the warranty start date.

[TripleTransAm]

Then when I got off the interstate I just had the radio, lights, and heat going, but the cooling fan was running (which is kind of funny, too. I have had that a few times this winter when it is 25 degrees or below and the cooling fans are running after being on the interstate for a while).


How did you detect the cooling fan was on?

[jgc61sr2002]

Cooling fans running. If you had the heater/AC control in the defrost mode I believe that activates the cooling fans.

[Eric91Z]

How did you detect the cooling fan was on?

I could hear it running. Again, couple times this has happened now this winter. Turn car off, back on, and no more cooling fans.

Drove car home from work and worked as normal. Even with the heat (on automatic), seat heater, and radio on. All was fine. Hoping it was just a fluke and not something possibly with the tune/ECM or beginning of electrical problem of some kind. Only other time the lights dim on me is at WOT.

The car is stock except for JLT CAI and XCal2 with Lidio's tunes in it. Currently running the 91 octane tune.

[merc6]

I had tha issue in broad day light if I stayed in drive. I raised the revs on Xcal2 and the needle sits hare north of 14

[Eric91Z]

I had tha issue in broad day light if I stayed in drive. I raised the revs on Xcal2 and the needle sits hare north of 14

I can't remember, but is idle speed one of the items that can be adjusted by the end user on the new models with that activated? I know mine has adjustability on it, but just don't remember what parameters are available.

As this is the first time it has ever happened, that I have been aware of, I think I will keep on eye on it. If it happens again, will bump the idle rpm up a little. If it continues after that, then stock program back in and in to the dealer.

[TripleTransAm]

Cooling fans running. If you had the heater/AC control in the defrost mode I believe that activates the cooling fans.


That's a darned good point. Defrost settings use the A/C compressor, and in some cases that kicks in the fan(s) right away. Good catch: the time I was referring to in my post above, I did have the system on Defrost!

As for the fans being audible, I have NEVER heard any of my fans running from inside the car, on either of my cars! And I'm usually pretty sensitive to my cars' operation. The only time I remember hearing my fans was when standing outside my car in spring 2003 while it idled in my driveway as I did something like check the oil or tranny fluid level or something. And I only noticed it because of the slight 'whoop' it did on fan shutdown, cycling every couple of minutes.

[Eric91Z]

That's a darned good point. Defrost settings use the A/C compressor, and in some cases that kicks in the fan(s) right away. Good catch: the time I was referring to in my post above, I did have the system on Defrost!

As for the fans being audible, I have NEVER heard any of my fans running from inside the car, on either of my cars! And I'm usually pretty sensitive to my cars' operation. The only time I remember hearing my fans was when standing outside my car in spring 2003 while it idled in my driveway as I did something like check the oil or tranny fluid level or something. And I only noticed it because of the slight 'whoop' it did on fan shutdown, cycling every couple of minutes.


It is really not a loud noise, just added white noise that I know if different than "normal". Can't say I heard them run all that much in September when it was still hot outside. Then again, I probably had the A/C blasting or windows down. Not loud or mechanical noise, just the added noise of a fan running.

[merc6]

I was in SAT texas with a/c on and on a hill behind that one bar and nissan dealership lil bit off huebler near I-10