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Old 09-30-2010, 09:46 AM   #1
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alternator not charging but checks good

Alternator not charging. 2.5 tj 1997 4 wire

I took it off checked connections, had it tested (ok), put back on, checked fuse (all good dont know what fuse is it anyway), checked big wire for breaks or loose.

With it running checked volts at alt output 12vto 11.8 (and at battery test same)

Checked v at the two small term. on alt , very low like .3 on one and 2 on other.

It has a new ecu, and wiring harness. gauge in display reads 12v, tach is working.

I dont know what else to check. I thought about tracing back the two feild wires back to the ecu for breaks. But that seems unlikley.

Considering just getting a external regulator and be done! crap! this is all that is stopping the jeep from getting out of my shop from a long engine rebuild.

Ideas of what else to check or ideas about the external reg.??

Lowell

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Old 09-30-2010, 10:09 AM   #2
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Alternator output should be approx. 14volts when running. If you are getting 12 volts at the alternator(running)it is not charging.

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Old 09-30-2010, 10:13 AM   #3
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Did it work (charge) with the old ECM? I think you have already figured out that the alternator's voltage regulator is contained within the ECM.
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Old 09-30-2010, 10:50 AM   #4
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Did it work (charge) with the old ECM?
No idea about that, this is the jeep I bought that was not running when I got it. The engine and alternator is all new (like new). I had autozone test it and it did great there.

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I think you have already figured out that the alternator's voltage regulator is contained within the ECM.
Yep in the ecu, why IDK but it is. Why cant they all be like the delcos?

I guess im gona trace the wire from the two field wires to the ecu to make sure they are right. I went to autozone this morning and they do have a generic regulator for 14.00 . I may do that as a last resort.

I was looking at the wiring diagram and the field wire from the gen is just one pin away from something called trans relay. That was listed in one of the codes thrown. Interesting because it is just one pin from the gen and the gen is not charging, and its 5 speed and should not have a relay Im aware of.

Going out to trace wires , I'll post back results
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Old 09-30-2010, 12:03 PM   #5
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Need a ECU? I got an extra ready to go if you need one, make me an offer.
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Old 09-30-2010, 12:12 PM   #6
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Need a ECU? I got an extra ready to go if you need one, make me an offer.
No thanks, maybe should have asked here b4. I just bought this new one for 225.00
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Old 09-30-2010, 12:22 PM   #7
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update wire tracing

I connected one end of the ohm meter to one of the field wires and the other to the plug pin. ( with battery cable off )

I get a good connection from each as I expected. I attached a crude drawing for future ref.



So I have found the following

The grey ECU plug #25 is the grn/org wire

The white ECU plug #10 is the green/blk wire

I m kinda running out of ideas, I knew the wires were ok, but had to check.

It may be time to connect seperate regulator, but I hate giving up on it.

Any other ideas???
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Old 09-30-2010, 02:10 PM   #8
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Measure the voltage from the batt (-) terminal to the alternator's frame, right on the alternator. Should be 0.

Suspecting a ground connection is bad. That makes the regulator "think" the battery is fully charged, and shuts down the alternator.
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Old 09-30-2010, 03:30 PM   #9
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Measure the voltage from the batt (-) terminal to the alternator's frame, right on the alternator. Should be 0.

Suspecting a ground connection is bad. That makes the regulator "think" the battery is fully charged, and shuts down the alternator.

Do you mean check for ohms at (-) battery to alternator frame. i.e. engine block.?
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Old 09-30-2010, 03:31 PM   #10
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put the meter on 12V and one end on alt body, and one end on the battery's negative post.
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Old 09-30-2010, 03:57 PM   #11
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Exactly, he meant to check for volts not ohms. Use the 12v scale, 25 volt scale, or whatever scale is closest to 12v without being under 12v. The presence of any voltage between the alternator body and ground indicates a faulty ground connection somewhere. You don't want to connect an Ohmmeter across anything that could possibly have voltage across it.
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Old 09-30-2010, 05:25 PM   #12
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Did that and nothing 0.
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Old 09-30-2010, 06:09 PM   #13
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That's while it's running of course.

Also leave the VOLTMETER connected the same way, shut it off, then restart it. It should remain near 0 even while cranking.

A bad or corroded mounting point of the alternator case or bracket can drive you nuts too.
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Old 10-06-2010, 07:36 AM   #14
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I put a different ecu on just to see. (it was off tj of unknow year or engine but looked the same) And walaa! the battery shows 14.4 volts. So that means it has to be the ecu. I dont know if I will contact the ecu people or just rig a external regulator.
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Old 04-16-2011, 12:41 PM   #15
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External Regulator

I have the same problem, did you end with an external regulator? If you did do you remember the part #?
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Old 04-16-2011, 09:42 PM   #16
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I put a different ecu on just to see. (it was off tj of unknow year or engine but looked the same) And walaa! the battery shows 14.4 volts. So that means it has to be the ecu. I dont know if I will contact the ecu people or just rig a external regulator.
if you just paid for that one better to get it replaced if faulty no telling when other issues will appear
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Old 04-17-2011, 11:12 AM   #17
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I have the same problem, did you end with an external regulator? If you did do you remember the part #?
No, I used a replacement ecu and it charges fine.

The one I looked at trying was at autozone. I just asked for a 3 or 4 wire regulator off a early chevy or ford. I think it would work. Only thing is the new regulator didnt come with a diagram. So you will need to hook it up corectly. Maybe find an old car and see how its wired. Do it wrong fry batt,alt,and maybe more.
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Old 04-17-2011, 11:17 AM   #18
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Quote:
Originally Posted by TOKKIE View Post
Alternator output should be approx. 14volts when running. If you are getting 12 volts at the alternator(running)it is not charging.
I'm going to guess that you all missed this post? An alternator that is not putting out at least 14volts isn't charging a damn thing.
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Old 04-17-2011, 11:59 AM   #19
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It's more complicated than that... if the alternator isn't being TOLD to charge, it will not charge. You just measure the battery volts. Found this out on another vehicle, newfangled hunky junky crapola... Too many other things involved for it to always be simple.
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Old 04-19-2011, 12:21 PM   #20
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TJ Alternator's have internal regulators so you can't replace them unless you tear it apart, I'm still willing to bet its the alternator. If they tested it and it's only putting out 12v or less it's screwed. An alternator on a test stand will easily put out 14.4v - 15v under load. So unless they took it out of the jeep and put it on a proper tester that puts a load on it it was not properly tested in the first place. At idle without a load it still should be putting out 14v. It's a TJ it's not that complicated.
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Old 04-19-2011, 12:28 PM   #21
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TJ Alternator's have internal regulators so you can't replace them unless you tear it apart...
The TJ alternator's voltage regulator is located inside the PCM on the firewall.
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Old 04-27-2011, 09:54 PM   #22
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Very interested in the results as I'm having the same problem. I'm not an automotive technician but I am an electronics tech. My 2002 TJ has a conventional regulator inside the alternator AND what could be considered another regulator inside the PCM. This is probably why I see so much disagreement on the web as to where a TJ's regulator resides. I don't have the factory service manual yet but I've got one coming. I've been able to figure out that the regulator within the PCM turns the alternator's field off and on by grounding one of the field wires.

With the Jeep running, I unplugged the 2-wire plug on the alternator then checked for 12V on both wires. One has 12V and the other does not. The one without the 12V is periodically grounded through an N-channel MOSFET within the PCM at up to 100 Hz with a duty-cycle of 25%, 50% or 100% depending on charging requirements. Remember what color that wire is. On my 2002 TJ it's green.

Next I measured the battery voltage and then temporarily grounded that green wire (disconnected from the PCM). Voltage jumped up to 14+ so now I know the alternator and internal regulator are good.

Under the battery is a temperature sensor that is fed directly into the PCM. Nearest I can figure, this is why there is a conventional regulator within the alternator and a pulse-width-modulated regulator in the PCM. This way they can regulate the charging voltage with the conventional regulator and vary the on-time verses off-time of the charging based on battery temperature to avoid overcharging a hot battery.

On my TJ the battery temp sensor goes from pin 4 of the black PCM plug (sensor ground) to pin 15 of the gray plug. The voltage at the grey plug varies as I cool and warm the sensor. Somewhere on the internet I read that this voltage should be between 0.5VDC and 4.5VDC. Mine's about 3.5VDC at ambient temperature so until the FSM arrives in my mailbox I'll assume the temp sensor isn't the problem.

I found a pinout of all 3 PCM plugs on the internet. I can't see where there would be any reason to keep the alternator field turned off other than too hot of a battery. No other pins appear that their inputs would effect battery charging so I ordered a rebuilt PCM.

I installed the new PCM and the battery started charging! Excellent!

Two days later it quit charging so obviously I haven't found the problem yet and the problem may be cooking PCMs. At this point I ordered the real service manual. I don't expect to see it for another week.

Please post your results and I'll do the same.
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Old 04-28-2011, 01:41 AM   #23
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.458 I am also an electronics tech and would love to see your pinouts/diagrams if you have them. Perhaps we can figure it out together.
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Old 04-29-2011, 08:27 AM   #24
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After replacing the alt & computer that didn't fix it I started thru the wire harness and presto, after a day or so I found a wire that had blown. Fixed it and the alt now maintains the chg in the battery. It was the solid green wire that goes from the alt to the computer and the harness had rubbed thru and then the wire......Jim
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Old 04-29-2011, 11:06 AM   #25
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Nice find Jim. That the harness had rubbed through the green wire is surprising. Was that part of the wiring still as the factory installed it and unmodified?
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Old 04-30-2011, 02:40 AM   #26
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Originally Posted by dannyobow View Post
.458 I am also an electronics tech and would love to see your pinouts/diagrams if you have them. Perhaps we can figure it out together.
dannyobow
I'm working off of the pin-outs I found on the internet and the partial diagram I've been drawing of the PCM using an ohm meter and downloaded semiconductor data sheets. I'd love to have a schematic of the PCM but I doubt that will ever happen. If the pics show up below you'll see how limited my information is.

When I first lost charging I got the "check engine" light. I borrowed a ScanGaugeII and pulled the two codes. P443 and P1495. An internet search revealed that they are both associated with the EVAP system circuitry. I also found out how the EVAP system works and pulled the Leak Detection Pump and Purge Solenoid out. Brought them in the house and hooked up to a 12 volt supply and vacuum pump and both work like they should. Checked all wiring too, both for continuity and shorts to ground.

I'm thinking (hoping?) that the original problem was crummy ground connectors under the hood that were screwed down to the firewall and hood (factory) without removing the paint. I've taken care of that. Remember, a new PCM brought back my charging but only lasted 2 days.

So here's what I've found inside the PCM. The field (green) wire to the alternator is periodically brought to ground through an N-channel MOSFET. It's a 30N06VL (red circle in pic) that was made by ON Semiconductor but is now obsolete. Motorola and Fairchild both make a substitute with identical characteristics and Mouser sells them for under a buck. This FET is gated off and on by a Texas Instrument 4-CHANNEL SERIAL AND PARALLEL LOW-SIDE PRE-FET DRIVER (green circle in pic) in a 24-pin DIP SMD with pins so close together I had to hone down the tips on my meter probes to keep from shorting 2 or 3 together.

There are 2 of these chips in the PCM. Using the plug pin-outs, a cheap Fluke meter and a bunch of patience I was able to figure out that one of them drives the 2 FETs that switch off and on the 2 oxygen sensor heaters and the other one drives the FETs that switch the alternator field and both EVAP components. Hey, now a picture is developing! One semiconductor is associated with both fault codes and my charging problem! Both PRE-FET DRIVERS are fed directly from one of the microcontrollers (purple in pic) that I haven't looked up yet and hopefully I won't need to.

Tomorrow I'll plug the PCM back into the Jeep and check for a signal at the inputs of the PRE-FET DRIVER. If there's a square wave there when the Jeep is running then I'll test the rest of the pins on the chip. I'm not doing all this work just for kicks. I can't afford a new PCM ever 2 days. I either need to be certain I've fixed the original problem or be certain I can fix the PCM if and when it fries again.
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Old 05-14-2011, 01:49 AM   #27
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UPDATE. Factory service manual arrived. If you aren't a mechanic, these things are great. They actually do a fairly good job of explaining how each system works. Their troubleshooting procedures are next to useless unless you have access to a DRB-III interface system but the manual is written for dealership technicians that have the tools.

Anyway, I'm charging again. I was successful at repairing the computer that died 2 days after I bought it. Before putting it back in, I removed the factory paint from under every ground connection I could find on both sides of the firewall. I hate intermittent problems

Since this PCM had the same symptoms as the original that blew, I'm assuming I can fix it for a spare.

Also, the FSM put me in my place. There is no regulator inside an OEM 2002 TJ's alternator. All regulation is done inside the PCM by controlling the duty-cycle of the MOSFET that grounds the switched field wire.
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Old 11-27-2012, 02:33 AM   #28
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Older post but common problem. I'm having the same issues. What did you do to your ECM for the fix? Cost?

I'd just bypass it and install a external regulator but for PA emissions you can't have a check engine light for any reason to pass.
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Old 12-04-2012, 12:57 PM   #29
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I replaced the part in the last picture (above) that I marked with a green dot. It was cheap. I bought it from Digikey.com for under $3. Part number is 296-10868-5-ND. If you are not an expert with a soldering iron then find someone that is. A desoldering station would be very helpful here but not absolutely necessary. I hope this post saves some of you a lot of money .
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Old 05-16-2013, 04:13 PM   #30
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After replacing the alt & computer that didn't fix it I started thru the wire harness and presto, after a day or so I found a wire that had blown. Fixed it and the alt now maintains the chg in the battery. It was the solid green wire that goes from the alt to the computer and the harness had rubbed thru and then the wire......Jim

Bumping old thread can someone tell me what green wire this is? Is it the one that plugs into the alternator that also has a pink wire with it?

This maybe my problem with my alternator not charging fully and dropping to 12volts then back to 14 volts.

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