External Voltage Regulator Location


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Old 04-14-2015, 03:31 PM   #1
ChicagOgre333
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Default External Voltage Regulator Location

Hi all, I have a 1991 XJ Briarwood 4.0L, 6Cyl that is currently killing my battery due to a bad voltage regulator, (Had my alternator tested twice just to be sure.)

When I asked for a replacement voltage regulator, I was given this:
Name:  Voltage Regulator.jpg
Views: 2237
Size:  92.8 KB

Unfortunately I was unable to find out where this goes. I looked on other forums and they have said it is either under the dash above and to the right of the accelerator pedal, or on the driver's fender under the hood.

I was unable to see anything under the dash that looked similar, but I did see this: Name:  ECU-PCM.jpg
Views: 3569
Size:  90.1 KB Name:  ECU-PCM location.jpg
Views: 1832
Size:  88.0 KB and was wondering if it might be inside it?

If you have any more info in this regard, please help! I'm dead in the water until I can get this problem resolved.
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Old 04-14-2015, 05:25 PM   #2
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I am digging trying to find out some info for you. Here are a couple wiring diagrams. I do know your pic is of the ECM (Engine Control Module, or computer) and the voltage regulator is "Built into" it. Around here a used ECM is 25.00 at a Junk Yard.




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Old 04-14-2015, 07:06 PM   #3
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All voltage regulation is done in the PCM on all Jeep vehicles from the late eighties to early nineties on forward. Whenever Jeep moved to Nippon Denso alternators, so It could be as early as 84; I just plain don't remember when.

Good Luck and let us know what you find out.

Are you certain that the voltage regulator is the problem?

You may be able to rig an external regulator up... i've just never attempted before.

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Old 04-15-2015, 10:33 AM   #4
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Thank you all for the replies so far, they have pointed me in a direction, but I still find myself hitting roadblocks to getting my XJ running again.

To answer your question, I believe it is the voltage regulator due to the guys at AutoZone testing the alternator once, while it was in the vehicle and their diagnostic tool saying the Volt Reg failed, and another AutoZone location testing the alternator removed from the vehicle and it passing. so based on their advice, I am assuming the problem to be the voltage regulator.

This morning I got up and removed the ECM/PCM from the fender of the car, and tried opening it to see if there was a voltage regulator inside of it similar to the top picture in my original post. (the triangular white item) this is what I found upon opening the housing: Name:  IMG_1110.JPG
Views: 1779
Size:  52.0 KB

It looks rather cracked and beat up and I don't want to try disassembling any further because, well frankly I don't have any star bolt drivers to remove those screws from the heat sinks. (also I am assuming they used those instead or regular screws to keep novices like me out of this piece.) I think I just need to replace the whole unit, what do you all think?

Thanks again, Good to hear from you all so quickly.

Last edited by ChicagOgre333; 04-15-2015 at 10:36 AM.
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Old 04-15-2015, 02:12 PM   #5
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Nice work! We like you already! I would recommend buying a used one from a local Junk yard. Install it and see if the problem is fixed. then I would try tearing the original one apart and try to fix it. BTW, Those star bolts are Torx. And the drivers or sockets are cheap and available at every auto parts store.

Back to your original problem. The battery draining overnite. What processes have you used to determine the voltage regulator is killing your battery? I just want to make sure you don't have a gremlin elsewhere.
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Old 04-15-2015, 05:33 PM   #6
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I think your's is in the alternator.


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Old 04-16-2015, 06:01 PM   #7
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^I think your right if that's the correct alt.
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Old 04-18-2015, 02:15 PM   #8
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Well I went and re-installed the alternator, and went and grabbed a junk yard ECU-PCM and installed it.

Unfortunately, I found (or created) a leak in my radiator that prompted me to remove the radiator and in doing so created a whole new problem for me. I'll post about that in the appropriate forum as it's cooling related and not pertinent to the electrical issue I am having.

To answer Gluckmysock's question about why I am assuming it to be my voltage regulator, the only info I have leading to that hypothesis is what AutoZone told me after testing my alternator twice.

I have been having issues with a security system and check engine light in my dash. the security system is a whole other ball of wax but it going off without provocation is what seems to be draining my battery and my alternator is unable to charge it up even when it runs for an extended period of time.

Hence why I went and had the alternator tested. First we tested it in the XJ with a full battery charge, and the handheld unit AutoZone used said that the volt regulator failed the test. Then we pulled the alternator and had it tested at a different AutoZone on it's in-house diagnostic machine and the alternator passed testing there.

It is a Denso Alternator so all info I have in regards to Denso alternators indicate the voltage regulator is located externally in the ECU-PCM.

- Jonathan
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Old 04-18-2015, 07:58 PM   #9
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Bummer about the radiator, leak issue. sometimes the more we fix the more **** breaks. It's definitely disheartening. But your support group is always here for ya!

Here is some more food for thought:












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Old 04-18-2015, 08:07 PM   #10
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And if all that doesn't blow you mind, how about this for shits and giggles!!


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Old 04-19-2015, 06:50 AM   #11
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On 91 its on the alternator. Its a 2 prong connector. Grab another alternator from wherever and try again
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Old 05-02-2015, 02:45 PM   #12
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I really don't want to remove my alternator again, it was a major pain and I'm relatively sure that since it is a denso not a delco the voltage regulator isn't it the alternator. I'm currently trying to replace my ground and positive battery cable and check all my fuses...a shot in the dark at the moment because nothing I have tried is seeming to help.
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