97 TJ Alternator Not Charging

[97TJHeadache]

I've scoured through all the threads on this forum and others to no avail. I'm looking for a direct answer on how to test the signal from the PCM to the alternator prior to shipping it off to WranglerFix.

Background:

Jeep sat up for a year as I was off on a private contract. I purchased a brand new PCM from WranglerFix about 2 years ago. Came home and had fuel pump issues, discovered a severed ground on the harness near the transmission. Problem solved. Jeep ran fine for about a 100 mile one way trip, then seemed to lose all battery power when I pulled into the driveway. Battery read 10ish volts on tester. A long diatribe of bs has happened since, so I'll just list what I've done so far...

1. Brand new battery
2. Brand new alternator
3. Checked literally every wire I can think to check and then some, no breaks. Loom running along stud at back of head is perfectly fine.
4. Removed, wire brushed/cleaned, and re-bolted block ground
5. Checked wire running from PDC to alternator, cleaned contact surfaces, re-bolted
6. All pins in PCM connectors look fine. No signs of corrosion
7. Temp sensor under battery seems fine. Wires connected. No breaks. Springs up like it's supposed to.
8. Replaced battery cables just because


So, at one point my PDC slid forward into the hot at the battery, sparking and blowing the #10 fuse. Replaced the fuse, Jeep ran fine. But this obviously concerns me as to what COULD have happened inside the PCM. Curious what experts think.

Otherwise, I've read that you can bypass the PCM signal and test for a voltage spike on the alternator. My Jeep is the 97 model, so keep in mind there is no standard "connector" and instead it has the power wire bolted in, then a small block like thing with two metal connectors in the center and two lateral wires that all 4 bolt down. Any help is greatly appreciated.

Edit* Forgot to mention, but when I replaced the battery the voltage gauge on the dash showed 12v, never going up to indicate the alternator charging, but on the trip home from the parts store the gauge dropped to minimum like it died and the check gauges light came on. When I got home and restarted the Jeep, the gauge worked fine again showing 12v. Still think the alternator may not be charging, but not sure if perhaps there's a short somewhere rather than it being a faulty PCM. I'm an electrical noob so explanations like I'm 5 are greatly appreciated.

 

[Chris]

I've scoured through all the threads on this forum and others to no avail. I'm looking for a direct answer on how to test the signal from the PCM to the alternator prior to shipping it off to WranglerFix.

Background:

Jeep sat up for a year as I was off on a private contract. I purchased a brand new PCM from WranglerFix about 2 years ago. Came home and had fuel pump issues, discovered a severed ground on the harness near the transmission. Problem solved. Jeep ran fine for about a 100 mile one way trip, then seemed to lose all battery power when I pulled into the driveway. Battery read 10ish volts on tester. A long diatribe of bs has happened since, so I'll just list what I've done so far...

1. Brand new battery
2. Brand new alternator
3. Checked literally every wire I can think to check and then some, no breaks. Loom running along stud at back of head is perfectly fine.
4. Removed, wire brushed/cleaned, and re-bolted block ground
5. Checked wire running from PDC to alternator, cleaned contact surfaces, re-bolted
6. All pins in PCM connectors look fine. No signs of corrosion
7. Temp sensor under battery seems fine. Wires connected. No breaks. Springs up like it's supposed to.
8. Replaced battery cables just because


So, at one point my PDC slid forward into the hot at the battery, sparking and blowing the #10 fuse. Replaced the fuse, Jeep ran fine. But this obviously concerns me as to what COULD have happened inside the PCM. Curious what experts think.

Otherwise, I've read that you can bypass the PCM signal and test for a voltage spike on the alternator. My Jeep is the 97 model, so keep in mind there is no standard "connector" and instead it has the power wire bolted in, then a small block like thing with two metal connectors in the center and two lateral wires that all 4 bolt down. Any help is greatly appreciated.

Edit* Forgot to mention, but when I replaced the battery the voltage gauge on the dash showed 12v, never going up to indicate the alternator charging, but on the trip home from the parts store the gauge dropped to minimum like it died and the check gauges light came on. When I got home and restarted the Jeep, the gauge worked fine again showing 12v. Still think the alternator may not be charging, but not sure if perhaps there's a short somewhere rather than it being a faulty PCM. I'm an electrical noob so explanations like I'm 5 are greatly appreciated.

To test the signal from the PCM to your alternator, you can follow these steps:

1. On your '97 TJ, the alternator typically has a plug with a few pins inside. Look for the smaller connector that delivers the signal from the PCM (Powertrain Control Module) to the alternator. Make sure you refer to your service manual for the exact pin layout and function.
2. Set a multimeter to measure DC voltage. You’ll be looking for a signal from the PCM when the engine is running.
3. Test for Voltage:
   - Start your Jeep and let it idle.
   - Carefully insert the positive lead of your multimeter into the signal pin of the alternator connector (you might need to back probe this if the connector doesn’t allow for probe access directly).
   - Ground the negative lead to a clean metal point on the engine or chassis.
   - You're looking for a voltage reading when the Jeep is running. Generally, you should see a voltage from about 5V to 12V depending on the PCM programming and the load on the alternator.
4. Bypass Test:
   - If you want to test the alternator directly, you can bypass the PCM signal. You can connect a wire from the battery positive (with the engine running) to the connector on the alternator that receives the signal.
   - If the alternator starts charging (you should see the voltage gauge rise and a voltage increase at the battery), then your alternator is functioning correctly, and the issue lies with the PCM or signal wiring.
5. Given your previous issues with grounds, ensure all ground connections related to the PCM and alternator are clean and have a solid connection. Sometimes, an intermittent ground could cause erratic behavior.
6. Since your PDC moved and sparked, it's worth double-checking that there are no internal damages to the PDC or any fuses/wires connected to it. Sometimes, a faulty relay could cause inconsistent behavior as well.

If after all this the alternator still isn’t charging and the PCM signal checks out, you might want to reach out to @Wranglerfix and have him run a test on your PCM for you. Electrical issues can be tricky, and testing thoroughly usually helps to isolate the problem. Good luck, and keep us posted on your progress!