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  #1  
Old 07-03-2015, 01:26 AM
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2004 Jeep Grand Cherokee Possible ECM problem

About 5 weeks ago, my voltage meter on my dash started going down. I automatically assumed alternator or battery. Took it to Autozone and had the battery tested. They said the battery was fine but there is either an issue with the alternator or ECM. To know for sure I would have to remove the alternator and bring it in from a bench test. Removed the alternator, took it in. Alternator is fine. So must be ECM. I bring the the alternator back home, put it back in my jeep. I start the jeep up just out of curiosity and bam the voltage meter is back where it should be right in the middle and everything is fine. Everything was fine for 5 weeks. Today, the voltage meter is back down around 9. I have checked my connections to the alternator, removed them, put them back on, still gauge reads close to 9. Unhooked the battery for a little bit, hooked it back up, still 9. So here is my question. Could the ECM still need to be replaced? Why would have it corrected itself after I took the the alternator off and then reinstalled a day later? Does pulling the power from it for a bit reset it or something? Before i buy a new ECM I want to explore all possibilities. Any suggestions?

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  #2  
Old 07-03-2015, 09:10 AM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Welcome to the garage.
Just a few days ago an other member had the same problem as you have, see here: 2000 grand cherokee 4.0 charging
This could well be the PCM, since the voltage regulator is inside. Also the voltage indication signal comes from the PCM. It could be that a power reset will reset something in the PCM.
Did you measure the voltage at the battery with the engine running? It most probably is well above the 15V? For some reason, the PCM is only seeing 9V at the battery and will increase the alternator field to try to increase the voltage at the battery. I donīt know where the PCM takes the battery voltage from, but it must be from PCM connector C1 pin 22 or connector C3 pin 12. I would remove those connectors and measure the voltage at those pins. If the battery voltage = voltage at those pins, then the problem should be inside the PCM.
I have attached the wiring schematic for your reference.
Attached Files
File Type: pdf Charging system.pdf (236.3 KB, 5 views)
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Old 07-03-2015, 01:12 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Yes it is measuring high at the battery. I am just going to order new ecm. I'm at 206k miles. Can't hurt to have a new one. If that's not the issue I can just begin to look elsewhere. Thanks for the info!
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Old 07-03-2015, 01:32 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Reverse trouble shooting (replacing parts first, then starting to measure) can be an expensive way to solve a problem. But keep us updated.
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Old 07-03-2015, 01:39 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Correction! I had my wife to sit in the jeep and watch the voltage as I jiggled some wires. Apparently the little plug that goes into the back of the alternator, with the green and white wires, is the culprit. As soon as I wiggled it the meter went back to 14. Now, I have no idea what this is called to buy a replacement. Any ideas?
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Old 07-03-2015, 01:54 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

There looks to be a little corrosion in the connector buts down in it and I can't seem to find anything to get it out. Looks like probably a cheap wire to replace. Am I right?
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Old 07-03-2015, 01:58 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

The small connector on the back of the alternator is for the alternator field feed. You can see it on the schematic i had attached in my first reply. But any bad connection there, would not explain a too high voltage at the battery, while the indication is still 9V.
Are you sure that the problem is the connector or wiring, and not the plastic part on the back of the alternator? The plastic part has the rectifier in it and the brushes, with some wire connections. This part can be changed separately from the alternator, when necessary. (did it on mine a few months ago)
If it really seems to be the connector or wiring, you have to make sure which of the two it is. If there is an internal wire breakage, you could splice a new in between.


---------- Post added at 02:58 PM ---------- Previous post was at 02:57 PM ----------

Quote:
Originally Posted by dustin2550 View Post
There looks to be a little corrosion in the connector buts down in it and I can't seem to find anything to get it out. Looks like probably a cheap wire to replace. Am I right?
You could try some electrical contact cleaner and after that some electrical grease for protection.
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Old 07-03-2015, 02:03 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Are you talking about the part the alternator that the field feed plugs into? How would I be able to determine that piece is bad by itself?
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Old 07-03-2015, 02:07 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

A good change that the corrosion you found in the connector is the problem, it will create electrical resistance. Use some electrical contact cleaner and see if that will solve the problem. If it does, then put some electrical grease on the pins to protect against further corrosion.
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Old 07-03-2015, 11:21 PM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

Ok look like the spraying didn't work. Still have to the wiggle the connection. Should I look at replacing the field feed on the alternator? I am unable to find that separate sold by itself to replace. Any Suggestions?
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  #11  
Old 07-04-2015, 07:42 AM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

It can be that the connector pin is corroded too much to make good contact and that it only will restore the contact by wiggling the connector. But are you sure the problem is the connector/alternator side, and not the wire itself?
If it would become necessary to replace the alternator side of the connector, i will give you an address on e-bay. They sell an alternator rebuild kit with bearings and the rectifier block for around USD 30. Do you have a Bosch alternator by the way?
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Old 07-04-2015, 10:06 AM
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Re: 2004 Jeep Grand Cherokee Possible ECM problem

It's a denso alternator. I'm Guessing it has at the connection.I've messed with the wire quite a bit and it seems to have no effect, only when I aggressively and forcefully wiggle the connection do I have any result. Can I buy the wire side plug and just splice in a new one? Along with the alternator side connector? Just to make sure I cover the whole connection?
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