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Discussion Starter · #1 ·
07 B9 with 73K miles

A few days ago, I got the warning lights on the dash of battery, brake, and rear diff temp. It was my battery and it was almost dead. My alternator tested on the car as a bad voltage regulator. I had replaced it 10 months ago with an aftermarket from O'Reilly's. I got the battery charged up and the voltage was 12.6 with the car running or not. The alternator was replaced under warranty.

I installed a new alternator and all connections and grounds were cleaned up. The new alternator is putting out 13.14 volts. I am reading it should be over 14. It seems to be charging the battery and I can run accessories. There are no warning lights now.

The kicker is that when I returned the old alternator, it bench tested fine even after it shows voltage regulator failed on the car. And the new alternator is testing on the car as voltage regulator failed.

Any ideas what could be causing the lower voltage on the car if not the alternator?

Thanks!
 

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interesting. is the tensioner and idler ok? i would look at the block grounds to see if they are corrosion free.

the batteries are quite petite in these cars. the first time the starter drags on a cold morning, i go get a new battery.
 

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Discussion Starter · #3 ·
Thanks! Yes the tensioner, idler pully and belt are all new this year. I saw one block ground On top and cleaned it up. It wasn't bad though. I will look for another ground.
 

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The below is going to get lengthy, so here's the executive summary: throw the A/M alternator in the trash; then go to a salvage yard, and get an OEM alternator off a junked Tribeca.



Assuming you've gone through all the usual stuff (checking for corrosion, loose connections, battery load/crank test, etc.), the problem is likely due to having an A/M alternator. Most alternators have some sort of voltage regulator, just as the Tribeca's OEM does. The difference is that, unlike many others, the Tribeca's OEM alternator is not "self-regulating"... the Tribeca has an IC regulator which receives an external signal from the ECM and, in response to that signal, manipulates the magnetic field of the coil causing the output voltage to fluctuate. A self-regulating alternator, on the other hand, typically is a solid-state regulator which essentially turns the alternator on or off according to the voltage in the system.

You can tell the difference between a self-regulating and external regulating by the number of wires to the alternator... a self-regulating alternator usually has only two wires, while an external-controlled alternator has three or more wires.

This is where A/M alternators can get tricky with the Tribeca... even if the A/M unit is capable of external control, the voltage regulator has to be "tuned" to the signal coming from the ECM, and my understanding is that this signal is not universal among manufacturers or even models (of the same mfg). That said, if you install a self-regulating alternator on the Tribeca, it will still put out a charge, but you're likely going to have issues at some point because the ECM and alternator are not communicating as they were designed to do, which usually leads to poor charging and/or other electrical issues.

Now, you might get lucky and find an A/M alternator that is externally controlled, perhaps even manufactured by the OEM (Mitsu), but AZ, PepBoys, O'Reilly's, etc. don't like to sell parts that fit on only one model of car (that would be a poor business model); they sell "universal" parts that are "compatible" with multiple makes/models. One potential problem with this is having a three-wire A/M alternator that does not manipulate voltage in the manner the external signal is calling for... for example, if the signal simply turns the alternator on/off (like the internal solid-state regulators) according to the external signal... if the Tribeca's ECM can call for varying levels of output from the alternator (e.g. low, medium, and high) but the externally-controlled A/M alternator only has two functions ("on" and "off") or more than three (high, medium-high, medium-low, and low), you can see where this is going to create a problem (imagine putting a dimmer switch on your starter). Of course, O'Reilly's can still sell this part to you and say it's a three-wire alternator which physically fits, but it won't function any better, and perhaps worse, than a two-wire alternator.
 

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I go on the theory that a bad alternator will take the battery with it and a bad battery will take the alternator with it. They are replaced in pairs if not caught early.

The bosch alternators in my other cars are quite simple. New bearings are twenty bucks tops and the regulator is about 30.

Not buying anything from FLAPs....priceless.
 

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Discussion Starter · #7 ·
Much appreciated! I have some homework to do. May be a few weeks but I will report back. Thanks for the info and advice.
 

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Discussion Starter · #8 ·
Thanks psygnal11!

Ordered a reman oem (Mitsubishi) from Maniac Electric Motors. $140 with 2 yr warranty. Puts out 14.6 v. Returned the aftermarket to oreillys and got my money back ($250). Much appreciated.
 

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Just incase anyone comes across this post looking for help, I had the same issues as cmurphy. Purchased an alternator from Napa for $240 and couldn't get it to work in my 07 Tribeca. Brought it back to Napa to swap it out and they ended up bench testing it and handed it back saying nothing was wrong with it. I screwed around with the car and had to hook it up to the charger nightly for about 2 weeks before I came across this post and ultimately purchased an alternator from Maniac Electric Motors - www.maniacelectricmotors.com for $140 that works flawless!
 

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Discussion Starter · #10 ·
Just incase anyone comes across this post looking for help, I had the same issues as cmurphy. Purchased an alternator from Napa for $240 and couldn't get it to work in my 07 Tribeca. Brought it back to Napa to swap it out and they ended up bench testing it and handed it back saying nothing was wrong with it. I screwed around with the car and had to hook it up to the charger nightly for about 2 weeks before I came across this post and ultimately purchased an alternator from Maniac Electric Motors - www.maniacelectricmotors.com for $140 that works flawless!
My reman from Maniac Motors is still working fine too!
 
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