Battery light on after computer replacement

[should of bought a 4runnr]

Yes I believe i have the answer.
I have a 2009 explorer with a 4.0
My dad bought a used pcm from a 2006 to swap in, same thing as others are experiencing battery light on
I have also tried a
I'll post some pictures of pinouts and the description of each years charging system, but what i came up with is that the smart charge system before 2009 and after 2009 is different.
The 2009 has a generator command wire and a generator communication wire and a b+ (battery voltage) so a total of 3 wires, it is my understanding that gen comm sends a signal of what the alternator is currently outputting and the gen com is telling it to change output based on demands from other parts of the vehicle (lights/ac/radio)
The 2008 down to 06 from research has a different charging system using only 2 wires, I'll post some pictures tomorrow and see. But I would check your pcm part number and tear tag and see if it is a pre 09 and you're putting into a 09+ maybe the circuit boards are totally different.
I'll post more on what I find.

 

[should of bought a 4runnr]

Came across this thread. Reppaced an ECM in a customers 2010 Ford Explorer V6 with a refurbished, pre programmed plug and play ECM online from Pro Tech Auto Systems. Vehicle originally had 3 hard codes for the EGR system. The PCM was the fix, as the codes went away BUT we ended up with a battery light ON and partial charging KOER 13.5V. Swapped original ECM back in, no battery light, charging just over 14V. Had company send us another ECM, same issue. Anyone come across a fix for this ??

Check to see what voltage you're getting at the alternator plug maybe back probed. Guessing it is like my post, and is a pre 09 pcm. Google the part number on it

 

[Yataku]

Hey everyone,

I came across this thread while browsing the forum. From my experience, this issue isn’t really related to the battery or alternator — it’s the PCM itself.

Ford had two main PCM models:

• One for 2006–2008
• Another for 2009–2010

The older PCM (2006–2008) can actually work fine on the 2009–2010 models, but with one small issue: the battery light stays on no matter what you do. From what I understand, there's a difference in voltage sensing between the two PCM versions. So when you use the older PCM in a newer car, it thinks there's a problem with the alternator or battery, even when everything is working fine.

I have a 2010 Ford Explorer, and when my PCM went bad, I replaced it with a used one from a 2007 model. It’s been about three years now — no issues at all, except the battery light has always been on so if you are have this problem no need to panic or spend money on replacing good working parts especially if it happened after your replaced the PCM then it's most probably what i have described here hope this helps

You can differentiate the two PCMs by their part numbers:

• PCMs for 2009–2010 start with 9L for an example see the picture below
• I don’t recall the exact part number for the 2006–2008 models, but it starts differently i think maybe it was something like 6L not sure tho

 

[should of bought a 4runnr]

Thanks @Yataku I have made a post about this as well recently since I had the same issue a few years ago when I started the same rabbit hole.