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Discussion Starter · #1 ·
I am hoping someone here can help with some troubleshooting. While driving in Chicago I90 traffic, I heard a screeching/static noise from under the hood or through the speakers, and the "voltage overload" warning message suddenly came on followed by the battery light and a "power system service urgent" message. It was nighttime and the battery died after driving about 30 more minutes. This week my mechanic installed a new alternator and he said it's working, but the power system service warning and battery light came back on. He's stumped and suggested pulling out the re-manufactured alternator that I bought and replacing it with a new Volvo OEM or Bocsh. He also mentioned that it was possible that some gauges could have been damaged due to a voltage surge, perhaps explaining why the power system service light came back on. If anyone here has any experience with this issue or knows some reasons why these lights would be on despite a functioning alternator, please help! Thanks.
 

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Had to replace ours about a year ago for the same reason. Unfortunately I bought and installed a new battery first before realizing it was the alternator. Got a new Bosch unit from RockAuto for a good price (with core exchange) and had it put in which solved the problem.

It's possible your remanufactured unit is faulty but I'll ask the obvious question first - have you driven enough to recharge the battery? If the battery is on the way out it's possible it won't charge up enough. I'd put a battery tester on it first and see if this is the problem before getting another alternator installed.

Good luck.
 

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I have learned, the "hard way", to have the supplier bench-test a reman alternator before leaving the store. Two, right out of the box, have failed this simple precautionary test. Even so, all in all, I have mostly had good service with reman alternators.
 

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There are two models of the alternator that are available for the XC90 V8 - a "self-regulating" and a "computer controlled" model. Externally they look identical. If you installed a "self-regulating" model and your car needs the "computer controlled" model, the alternator will still work fine, but you will forever get the "Power System Service Urgent" message. You can check for proper alternator operation by checking the battery voltage while the car is on and running. It should be around 14v. If it reads 12v or less, the alternator is not operating.

Once a correct "computer controlled" alternator is installed, the Power System Urgent message will go away on it's own. It does not need to be "reset".

I would check to see the exact model number of the alternator that you had installed.

2005+ models with the "computer controlled" output is Bosch part #AL0821X (AL0821N if new, AL0821X is reman)
2003-2004 models with "internally regulated" output is Bosch part #AL0820X (AL0820N if new, AL0820X is reman)

I'm betting your mechanic put in the 2003-2004 model with model number AL0820X or AL0820N with the internal regulator. Like I mentioned above, it'll work, but you'll forever get that message and it's not ideal.

I recently went through a V8 alternator failure as well: http://andrewpeng.net/cars/2006-volvo-xc90-v8-awd/alternator-replacement

best of luck, hope this helps.
 

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Discussion Starter · #5 ·
Guys, thanks for the suggestions. Today my mechanic installed a second alternator, this time Bosch part #AL0821X. The power service and battery lights are still on! He said the alternator is working, as was the the first one he installed, measuring just under 14 volts. This is getting more and more frustrating. :mad: I guess a very expense trip to Volvo is in my future. But what are they going to do? Tell me I need to install a third, brand new Volvo alternator? ANY other ides why the service lights could be on despite a functioning alternator?:confused:
 

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Guys, thanks for the suggestions. Today my mechanic installed a second alternator, this time Bosch part #AL0821X. The power service and battery lights are still on! He said the alternator is working, as was the the first one he installed, measuring just under 14 volts. This is getting more and more frustrating. :mad: I guess a very expense trip to Volvo is in my future. But what are they going to do? Tell me I need to install a third, brand new Volvo alternator? ANY other ides why the service lights could be on despite a functioning alternator?:confused:
I hate to say this, but if your alternator failed by outputting excessive voltage (As indicated by the Voltage Overload message you got) there is a possibility that other electronic components were damaged. If the alternator is "working" and you know you got a good one, it's time to trace the wire harness back and start checking components as you follow it back to the computer.
 

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There are two models of the alternator that are available for the XC90 V8 - a "self-regulating" and a "computer controlled" model. Externally they look identical. If you installed a "self-regulating" model and your car needs the "computer controlled" model, the alternator will still work fine, but you will forever get the "Power System Service Urgent" message. You can check for proper alternator operation by checking the battery voltage while the car is on and running. It should be around 14v. If it reads 12v or less, the alternator is not operating.

2005+ models with the "computer controlled" output is Bosch part #AL0821X (AL0821N if new, AL0821X is reman)
2003-2004 models with "internally regulated" output is Bosch part #AL0820X (AL0820N if new, AL0820X is reman)

I'm betting your mechanic put in the 2003-2004 model with model number AL0820X or AL0820N with the internal regulator. Like I mentioned above, it'll work, but you'll forever get that message and it's not ideal.

I recently went through a V8 alternator failure as well: http://andrewpeng.net/cars/2006-volvo-xc90-v8-awd/alternator-replacement

best of luck, hope this helps.
Are you sure those 2 are interchangable? the AL0820X is for the 5/6 cylinder engines pre LIN bus....
ALL V8's use a computer controlled (LIN) alternator. Where did you get info saying that some dont?
 

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2005+ models with the "computer controlled" output is Bosch part #AL0821X (AL0821N if new, AL0821X is reman)
2003-2004 models with "internally regulated" output is Bosch part #AL0820X (AL0820N if new, AL0820X is reman)

I'm betting your mechanic put in the 2003-2004 model with model number AL0820X or AL0820N with the internal regulator. Like I mentioned above, it'll work, but you'll forever get that message and it's not ideal.

I recently went through a V8 alternator failure as well: http://andrewpeng.net/cars/2006-volvo-xc90-v8-awd/alternator-replacement

best of luck, hope this helps.
I just pulled the bosch ID spec info and wow, they are totally different!
now i really wanna know where you got this information!!!
 

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Discussion Starter · #12 ·
I fixed my problem by changing the regulator to the one that was on the old alt.
I was thinking of trying that but concerned that my alternator failed because the regulator itself went bad. I read somewhere that most of the failures are due to a bad regulator. I dropped my car off today to have some diagnostic tests run by a Volvo technician. I should have information tomorrow. I'm starting to wonder if the re-manufactured alternators I bought had bad regulators and possibly that's why they were working/charging but not communicating correctly.
 

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I'm not 100% sure what the failure is - if it were the regulator unit I would hope to see more retailers selling just the regulator instead of shipping out a large and heavy complete alternator unit.

I couldn't tell on mine because a prior oil leak had caked the alternator in oil. There's no telling exactly where it failed; all I knew is that it failed because a few quarts of dirty oil dripped onto it and then got baked on by heat.
 

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Discussion Starter · #14 ·
I learned today that the following Diagnostic Trouble Code is active "ECM-U012087 Lost Communication with Starter/ Generator Control Module. Bus Signal / Message Failures. Missing message"

Anyone here know about this code or have any ideas? What exactly is the Starter/ Generator Control Module?
 

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Discussion Starter · #16 ·
Disconnect the small wire from the alt and check voltage key on.
Check the terminal on the alternator with that wire disconnected as well and report back.
The voltage at the small wire was .15 (minimal) and the battery voltage was 13.6 with and without the small wire connected. I was told that the small wire is a communication wire and that the voltage should be minimal.
 

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Each module on the LIN bus (ECM and ACM) sends out a refrence voltage just under battery voltage (volvo says 8-b+). The master (ECM) grounds out the refrence voltage to start communication, then the slave (ACM) responds by also grounding out that wire. The grounding is quick square wave pulses.
It sounds like you will need an ECM...
 

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Discussion Starter · #18 ·
Each module on the LIN bus (ECM and ACM) sends out a refrence voltage just under battery voltage (volvo says 8-b+). The master (ECM) grounds out the refrence voltage to start communication, then the slave (ACM) responds by also grounding out that wire. The grounding is quick square wave pulses.
It sounds like you will need an ECM...
Thanks for the info. If the fault is with the ECM, do you think is it possible that the trouble code would be isolated to only the one that's active (ECM-U012087)? Before your analysis I was thinking that if the ECM is the problem there would have been other trouble codes active when the diagnostic scan was performed. I was also thinking it would be some coincidence for the ECM to fail exactly when the alternator did, unless high voltage fried the ECM - but then why wouldn't there be any other codes or problems? I've been driving the car for over a week now with the light on, with no other issues yet..
 

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Discussion Starter · #19 ·
Problem solved :)

The analysis/info provided by garbergtsi was right on. The ECM was the problem. The dealer wanted $1,800 for a new ECM and programming. I declined and purchased, via Ebay, an ECM repair service from a company called XeMODeX. I called the company first and spoke with a technician. Apparently failure of the alternator ECM circuit in XC90 v8s is common - something about the circuit being too weak for the voltage it handles. The technician said the circuit they install has 3x the capacity so it can handle higher voltage and heat. The ECU sits on top of the air filter and took all of 1 minute to remove. It took exactly 1 week from the date of shipment to XeMODeX (in Canada) to when it was returned to me today! No more warning message, red triangle or battery light!! The repair w/shipping cost $350 total. No need for reprogramming because this was a hardware fix only. I ended up with an extra brand new Volvo voltage regulator. If anyone needs this part, send me a PM and I'll give you a good deal.
 
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