Fusible link blown- possible malfunction in ECU? - Jeep Wrangler Forum
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Old 08-28-2012, 03:43 PM
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Fusible link blown- possible malfunction in ECU?

Hey, new jeep owner here, I've got a 2002 wrangler, and it started throwing up a check gauges warning, and I noticed that the voltage was at ~12V.

A bit of sleuthing with a multimeter turned up that the fuse between the alternator and battery is blown, the alternator's end of the fuse reads 26V while the battery's end reads 11.5V.

Am I correct in guessing that this is a malfunctioning ECU, or is this a simpler, less expensive fix?

Also, the fuse is apparently a 12V, 50A fuse, shouldn't the voltage to the battery be 14V?

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Old 08-28-2012, 04:41 PM   #2
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26 volts is very high for an alternator output. I would use your meter to test the voltage output cable at your alternator - red lead to the bolt holding the red alternator cable on, and black lead to the battery ground. Are you seeing 26 volts here?

I also own a 2002 with the 4.0L, and recently changed all of my battery cables out for thicker ones; I am not sure which fuse you are referring to, as my alternator output cable runs to the fusebox, but it is in a common terminal with the fusebox's battery supply. In other words, there didn't appear to be any sort of fuse inline between the alternator and the battery.

Also, have you had your battery load tested? A weak battery will not filter the excess voltage the Alternator puts out, so you can get really high or really low voltage ratings from a bad battery.

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Old 08-28-2012, 05:52 PM
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That's where I got the 26V reading from. And I just checked, and noticed that the red wire from the alternator actually leads to the fuse box, not the battery. So there appears to be a fuse before the fuse box?

As to load testing, I haven't had tested this battery.
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Old 08-28-2012, 06:57 PM   #4
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If your alternator is putting out 26v take it out, have it tested, and when the regulator fails get a new one. Youll already be at the part store. =)

Thats my guess, anyhow.

Yes, all automotive fuses should be 12v, even though alternators can put out nearly 15V regularly without damage. It is still referred to as a 12 volt system.
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Old 08-28-2012, 07:04 PM   #5
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The cable that connects the alternator to the fusebox is crimped into a common connector with the cable that runs from the battery to the fusebox. There is no fuse inline, therefore the alternator is electrically connected directly to the battery.

I would be willing to bet that BlueRidgeYJ is correct and that you have a bad alternator. They have voltage regulators and yours appears to be toast if you are getting 26 volts out of it. I am actually surprised your battery hasn't exploded to be honest.
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Old 08-28-2012, 07:23 PM   #6
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Quote:
Originally Posted by eboven
... I am actually surprised your battery hasn't exploded to be honest.
+1

As far as that fuse, 12vx50a=600watt, run 26v and it becomes a 23A fuse, if all things were the same, which they arent. Whatever that fuse goes to, it saved it from cooking.
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Old 08-29-2012, 10:42 AM
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Took the alternator to the parts store, checked out fine. While I was there, I picked up another fuse, and on a whim, I put the new fuse in. It works fine now, apparently the alternator doesn't regulate properly if there's no load.

Also, when I was at the parts store, I realized that the alt can put out a lot more power than 600W, so I probably just tried to draw too much from it.

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