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2007 Explorer Alternator/ECU Question

wmkube

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City, State
Lucas, TX
Year, Model & Trim Level
2007 Explorer - standard
Question - on my 2007 Explorer, is the alternator charging controlled by the ECU?

Background - 2WD, 4L V6. About 160K miles. 2 or 3 months ago, the original alternator faded away. Understandable, with that many miles. Went to O'Reilly Auto Parts and bought a reman alternator, installed it, and everything worked fine. Alternator/battery voltage measured 13.5-14 volts, depending on engine RPM and battery charge state. Last week, it died on my wife on her way into work. I was out of town, so my son rescued her and got a new battery at WalMart. WalMart said the battery probably wasn't bad, just needed to be charged, but they gave her a free one under warranty anyway.

I had her go by O'Reilly to have the alternator checked to make sure. Well, there was no alternator charging voltage at any RPM. The Explorer was only operating on the battery voltage. So she parked it at home and drove our other car while I was out.

Today, I removed that relatively new (rebuilt) alternator. O'Reilly checked it, and it failed the test. No problem, gave me another reman alternator under warranty. Brought it home, put it on the Explorer, and no charging. Crap! Took it off, back to O'Reilly, and they tested it and it passed fine.

Looking further into it, I believe the problem is with the "I" (indicator) input to the alternator. Everything else tests out fine - the mega fuses are fine. All of the fuses in the fuse box are good.

The alternator has 2 plugs plus the large red output lug. The larger plug has 3 wires - red on "A". green on "S" and yellow on "I". The green "S" wire loops externally to a single wire plug that goes back into another connector on the alternator.

I've not been able to find a wiring diagram on line specific to the 2007 Explorer. Earlier diagrams show the "I" wire connected to switched 12 volts through the charge indicator lamp on the dash. I'm familiar with alternators to know that's the reference voltage back to the alternator's voltage regulator to tell it how much to charge. But the 2007 Explorer doesn't have an indicator lamp (idiot light).

If I unplug the 3 wire connector and read the voltage on the "I" pin (yellow wire), there is no voltage there whether the ignition is on or off. If I start the engine and apply an external voltage (using a Power Probe) to the yellow "I" wire, then the measured voltage at the battery immediately rises above 13 volts, and I hear the engine RPM drop slightly from the alternator load.

Without a 2007 specific wiring diagram, I can only guess that the "I" wire is connected to (and controlled by) the ECU. My other guess is that when this recent alternator failed, it caused a problem in the ECU. Unless there's a fuse somewhere in that "I" line (he says hopefully). I'd really rather not have to replace the ECU, but I gotta have this car working for my wife.
 
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AlienMartian

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No one has answered this in nearly 3 years? Seriously? I'm having the same issue at the moment. I pray you happen upon this and can tell me how you resolved it.
 
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D Hook

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Here's a website that explains the three wire system:


Had alternator problems recently and also suspected the ECU but when looking at the wires going into the harness, found only two wires on mine instead of three. Not sure why. But after replacing the alternator all the problems went away. I would say the OP just happened to get a couple bad alternators for O'Reillys. I went with the Carquest brand.

Other info on this thread: What brand alternator is recommended? Reman or rebuilt?

I did some other research on this but I'll have to dig around for it.
 
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