Alternator issue? Or FICM?

[BlkSC]

Ok, in the last three months, when I start my truck cold, from time to time the battery light will come on for a minute or so and then go out.

So I put my battery voltage and FICM voltage on my Edge CTS, the battery voltage will vary between 11.8 to 13.8 and the FICM voltage, on cold start up, will be around 43-45 volts and after a bit comes up to 46.5-48.5 volts.

Tonight I went out, and with the truck cold, the key on, engine off FICM voltage never dropped below 46 volts and my batteries with the engine off read 12V. With a meter, the batteries read 12.6V. After starting it, the Edge CTS was still reading .5 to .6 below what my meter read.

I tested the FICM with my meter before doing the PHP FICM remote reprogramming about 8-9 months ago and it tested fine, not saying it couldn't be starting to go bad. So what do you guys think? What do you think my next step should be?

[BlkSC]

Any ideas?

[Lilpooh]

Check the amps on the alternator, your gonna need a clamp on amp meter. At idle, the amps should be around 60amps with the factory 110amp alternator.

[FourFun]

My gut tells me alternator. It's fighting and probably on the brink...

[a2elvis]

Yep sounds like alternator is going... Replace it before it dies completely

[squirtgun]

Having a similar issue with my truck.Cold starts that will shake your teeth and the battery light flickers a few times.I just replaced the alternator in march and had it check about 2 months ago when I replaced the idler pulley.
I guess I'll be pull the alternator and getting it checked

[Fishermedic]

Am I missing something here? I'm not very mechanically inclined and trying to learn as I go here so bear with me...

From what the OP said I don't see a battery voltage/alternator problem, I see an FICM voltage problem.
From my limited knowledge bat volts at 12 KOEO is good, starting they drop to 10-11 and then come up to 12-14 KOER. If the bat voltage was staying low KOER I would think alternator.
FICMV at 48 KOEO and above 45 starting and running. FICMV below 45 on a cold start tells me that the FICM is on its way out.

So what have I missed or what do I have messed up here?

[Lilpooh]

Originally Posted by Fishermedic

Am I missing something here? I'm not very mechanically inclined and trying to learn as I go here so bear with me...

From what the OP said I don't see a battery voltage/alternator problem, I see an FICM voltage problem.
From my limited knowledge bat volts at 12 KOEO is good, starting they drop to 10-11 and then come up to 12-14 KOER. If the bat voltage was staying low KOER I would think alternator.
FICMV at 48 KOEO and above 45 starting and running. FICMV below 45 on a cold start tells me that the FICM is on its way out.

So what have I missed or what do I have messed up here?

The FICM needs to be tested with good batteries and charging system, if he has weak batteries/alternator, he will get a weak FICM volt.

This is where the OP needs to check all his battery cable connections (at battery and to the motor) for corrosion/bad connection. Load test the batteries separately and test out the alternator amp output.

[Fishermedic]

Got it.

I knew that the batteries needed to be checked first but didn't think about the alternator. I was thinking that since the battery voltage was recovering quickly to where it should be while the FICM voltage was staying low the FICM would be the more likely problem.

I'm still learning to trouble shoot mechanical problems I guess. I already know that all possibilities need to be addressed before you know for sure what the problem is and what parts need money thrown at them AND if you don't do this you'll spend more money than you need to. Thankfully I haven't learned it from my own experiences but if I don't learn to check all possibilities every time (even when I think the problem is fairly obvious) I will have the experience first hand. Thanks for the help Lilpooh.

[BlkSC]

Ok, here are my test results on my alternator.
On startup, batteries read 12.6V. After startup, no amperage for a minute or so which I understand is normal. With no load, the amperage then goes up to 70A and then will start to drop, I stopped watching when it got down to 40A and that's at 13.8-14V. With the AC and lights on, the amperage goes up to 72A and the voltage drops to 12.8-13V. This is all at an idle, do all these values seem ok? The voltage dropping to 12.8-13V at idle with the loads on kind of seems low but I'm not sure.
And would any of these readings explain my FICM voltage variance?