Bad PCM? Alternator isn't charging

[JKP]

I would take the alt to a parts store or local starter/alt shop and have it checked out for free.

If good, it points to the PCM.

 

[ItchyDong]

Jump 12 volts to the field wire input giving it "full field" with your permanent ground installed with a DVM installed on the battery. The second you supply 12 volts to the field input, your DVM should jump to something like 14 volts.

Edit: What year is your Jeep?

 

[f22beaver]

I would take the alt to a parts store or local starter/alt shop and have it checked out for free.

If good, it points to the PCM.

I took the old and new alternator and they both load tested as good.

Jump 12 volts to the field wire input giving it "full field" with your permanent ground installed with a DVM installed on the battery. The second you supply 12 volts to the field input, your DVM should jump to something like 14 volts.

Edit: What year is your Jeep?

Hey there @ItchyDong (love the user ID BTW), mine's a 2004. Just for clarity, when you say permanent ground you're referring to? The alternator itself is just ground through the mount and the source and field both go through the PCM. This is probably the only test I haven't completed.

 

[ItchyDong]

I took the old and new alternator and they both load tested as good.

Hey there @ItchyDong (love the user ID BTW), mine's a 2004. Just for clarity, when you say permanent ground you're referring to? The alternator itself is just ground through the mount and the source and field both go through the PCM. This is probably the only test I haven't completed.

I took the old and new alternator and they both load tested as good.

Hey there @ItchyDong (love the user ID BTW), mine's a 2004. Just for clarity, when you say permanent ground you're referring to? The alternator itself is just ground through the mount and the source and field both go through the PCM. This is probably the only test I haven't completed.

Sent you a PM

 

[Jerry Bransford]

It's still looking like a bad voltage regulator inside the PCM.

 

[Albertabackroad]

@Albertabackroad so long as you meant female plug 2 to battery ground then the resistance on that is 870 Ohms. It's also 870 to the engine block ground. Sounds like I need a new ground from the engine block to the plug. You know how to open up that type of plug so I can pull out the existing green wire?

I got the wire pulled. I'm still looking to understand the difference in diagrams. Mine says the field goes to the PCM, @Albertabackroad diagram says it goes to ground.

Yea the diagram I sent you is dealership OEM info. The wire you measured 870 on (the ground wire) has a break/corrosion somewhere. Last one I fixed I just cut relatively close to the plug, joined onto it and ran it directly to ground with an eyelet. No need to try and remove the pin and whatnot. If you want to be certain, you can measure resistance from the pin, to about 2” down the wire just to make sure you’re not joining into a bad point. Ezpz

 

[Mik]

Not sure where to put this but a big shout out to Wranglerfix for my installed new pcm. With a ton of $$$ trying to fix codes, stalling, and pretty much a dead jeep the installed new pcm instantly made everything perfect.

 

[Wranglerfix]

Not sure where to put this but a big shout out to Wranglerfix for my installed new pcm. With a ton of $$$ trying to fix codes, stalling, and pretty much a dead jeep the installed new pcm instantly made everything perfect.

Thank you very much, sir! We earn our reputation one pcm st a time and greatly appreciate your review.

There is a Wranglerfix Google page that could use a review if you would be so kind. I dislike them as much as the next guy yet it helps with algorithms. We think we’re searching Google and it’s just the opposite.

 

[Mik]

Done, thank you!

 

[Rygrego]

Measure resistance between the ground terminal at the alternator, and battery ground. I’d say the ground is bad. Most of these Jeep’s are grounded on the side of the block. If resistance is high, run a new ground.

The ground on the alternator is the case , no terminal.