Not Charging (ECM Replacement?)

I

IdahoWoody

New Member
Supporting Member
Joined
Nov 28, 2021
Messages
18
Location
Kuna, Idaho
As with similar threads on the forum, my check light has come on and the voltage gauge starts low then drops to zero. I have confirmed the battery is not charging. Following advice from the threads I have read through here I have checked the battery, cleaned and re-connected the battery, cleaned and reset every ground I could find and had the alternator bench tested at 3 separate parts shops (tested good). So now, at at the point of turning to the ECM thinking of regulator. My questions are:
1) Am I headed the right direction - is the ECM the next logical step or are there other steps I should pursue first?
2) If ECM is the next step - any suggestions on where/how to purchase a new one so I get the right component and dont screw something up?
3) There are a number of comments about an external regulator setup - is this a better way to go? If so, any links to a good instruction set a dummy like myself can follow?
Thanks in advance for your help...
 
With the vehicle running, backprobe pin 1 (white with dark blue trace) at the alternator. You should have 12 volts. If not, either it's a broken wire or bad PCM.

If you have 12 volts at pin 1, with the vehicle running, install multimeter on battery set to volts DC. Backprobe pin two (Dark green) and give it a ground with a test light or jumper wire connected to battery ground. If your multimeter jumps to 13.5-14 volts, either you have a broken wire, or a bad PCM. If voltage doesn't jump to 13.5-14 volts, you could have a bad alternator.

Do that and let me know what you find.
 
Last edited:
  • Like
Reactions: Wranglerfix and SoCalGlide
Two additional things to check...
Disconnect the three 32 pin harness connectors from the ECU and check the pins/clips for oxidation; then firmly snap the harness connector into the ECU receptacles.
Thoroughly inspect the wiring harness that is routed around the back of the valve cover which curves around a threaded head stud in the right rear corner of the head. The threaded head stud is known to rub thru the harness split wire loom and wiring insulation causing communications between the ECU and sensors to short to ground.
 
  • Like
Reactions: ItchyDong
IdahoWoody said:
Will take a look, many thanks!
Click to expand...
You also need to google how to backprobe. You want to test the circuit while it's "loaded". Get a t-pin, or a paperclip to slide in the backside of the connector for both of these tests. The connector has to stay plugged into the alternator during testing.
 
Last edited:
Your Jeep also utilizes the battery temp sensor in the charging circuit. Testing on that needs to be completed as well before you deem either the alternator or PCM faulty. Start with what Charles and I suggested first, we'll move on from there.
 
Unfortunately, I am still not able to identify the pins in the back of the alternator. Pulled the alternator again to get the attached image. Only wire connections are the main power lead and the two field leads at the bottom. I cannot discern the color of the wires going to the field leads? Pulled the three ECU connectors, they looked really good. Re-seated. Checked the harness in the back of the valve cover, and although a bit cracked, looked good and wiring inside undamaged. Put everything back together and still no go on the voltage.

jeep alternator.jpg
 
Th
IdahoWoody said:
Unfortunately, I am still not able to identify the pins in the back of the alternator. Pulled the alternator again to get the attached image. Only wire connections are the main power lead and the two field leads at the bottom. I cannot discern the color of the wires going to the field leads? Pulled the three ECU connectors, they looked really good. Re-seated. Checked the harness in the back of the valve cover, and although a bit cracked, looked good and wiring inside undamaged. Put everything back together and still no go on the voltage.

View attachment 295270
Click to expand...
Well, that’s not the alternator that my print showed and I’m away from my computer now.
 
CharlesHS said:
The regulating of system voltage and charge is done by the ECU.
Click to expand...
So what’s that big black block on the back of his alternator? I understand the two wire set up just fine, but where do you find a print showing his set up? I looked at 97 wiring diagram to give him his advice.
 
Top Bottom
Back