Hi all,

My daughter has a 2011 Volvo S80 3.2L. Last week when driving home from work, the car stalled out. We had AAA tow it to a shop I regularly use who told us that the alternator was bad and that it would be about $1250 to change it out. I decided to have it towed back to my home so I could do the work myself.

I picked up a remanufactured 180A alternator from O'Reilly's (Ultima I think was the brand) and set to work on taking out the intake manifold and swapping out the alternator.

After I got it all back together, the battery was not charging. I did a cursory check on the wiring, cleared codes from the computer, took it for a spin around the block, and then checked everything with my multimeter. Voltage between the B-post and ground was essentially the same as battery voltage, so clearly we weren't getting any current from the alternator. Continuity was good from the B post to the positive battery terminal, so I suspected we weren't getting the field on the rotor energized.

I limped it over to a mechanic a few blocks away from my house to have him take a gander. He pulled up the wiring diagram and noted that the two pin connector which energizes the field has one pin getting battery voltage of 12V and one pin connected to the ECM, presumably to allow it to use PWM to ground the pin to manage the output of the alternator. The pin on the ECM is A92, which goes to pin 1 of the alternator connector via a blue wire with a brown stripe. He told me he suspected the ECM was bad and wouldn't touch a Volvo computer. He didn't even charge me, just told me I should take it to the dealer and see how it goes.

Trouble is...there doesn't seem to be a Volvo dealership close by - nearest one is about 25 miles away, next closest is 28 miles in a different direction. Not sure I could make it that far on a single charge of the battery...

I pulled the connector off the ECM and, with the car off, put a small wire into the wiring harness at pin A92. I was able to measure 12V between the harness and ground at this pin, which suggests to me that the rotor wire is connected to power. I was also able to check pin A92 at the computer with the car off and with the ignition on (but obviously not with the car running) that the pin was not grounded.

I would like to verify that the alternator is good by jumping pin 1 on the alternator connector to ground (or pin A92 in the ECM wiring harness) to give full field and verify that doing that gives me a charge. That would for me confirm that the ECM is the problem. However, I would prefer not to have to remove the intake manifold again to get to the alternator connector. However, I can't figure out a good way to un-plug the connector. I can reach it if I go in through the side by the power steering reservoir and dipstick, but I can't seem to work the latch to get the connector off. I also can't think of a good way to splice into the computer's connector without risking a bent pin or short.

Has anyone out there managed to get the alternator connector off without taking off the manifold? I am considering maybe just loosening the manifold without taking it off so that I don't have to muck with all the electrical connectors and seeing if that gives me enough wiggle room. But before I try it, I thought I'd see if anyone else has any good ideas.

Much appreciated in advance!

Andre

 

OK - stop thinking blue wire pinxx/ecm/something complicated. The most common reason the alternators do not charge on the 6 cyl - is they are not spinning - and it's hard to see they are not spinning with everything put together.

The one way clutch on the alternator seizes and pulls the drive gear loose. So - the alternator drive gear is loose and does not spin the alternator. You put a new alternator on and it still does not charge the battery. Did you check to make sure the drive gear was tight? Was the one way clutch on the old alternator working properly? If it would not freewheel one direction - it was bad, and pulled the drive gear loose.

My first tech that encountered this was fooled by it - we eventually put the old alternator back on with a new clutch and secured the drive gear to make the system work properly.

 

Thanks for the thought and the reply. I did check that the drive gear was solid and tight when I put on the new alternator. Could not spin it at all. I also have verified that the gear sleeve coupling is spinning with the engine running by lightly touching with a bent wire probe. I can both feel and hear it rubbing as it spins. The new alternator is definitely spinning.

That said, there does not appear to be a clutch involved, at least on the alternator side. The rotor seems to turn with the gear on the alternator no matter which way it is turned. This was the case with both the old and the new alternator.

 

The 6 cylinder alternators have an overrun clutch - if the engine slows down rapidly - the alternator is allowed to keep spinning. If not the mass of the armature is enough to spin the drive gear - which has no key way - it just slips and loosens the securing bolt due to the direction it is spinning.

The clutch look like this

https://www.eeuroparts.com/Parts/809...BoCTqEQAvD_BwE

 

That makes sense. In any case, the drive pulley was solid when I changed the alternator.

 

On a whim, I grabbed the old alternator and pulled off the voltage regulator. Using my multimeter, I can see that the 1 and 2 pins of the connector are definitely not connected to the rotor's brushes/slip rings etc. This raises a bunch of questions for me.

Does anyone know how this voltage regulator is supposed to work? My mechanic did mention something about the ECM putting out 3V on pin A92. Is this supposed to be a signal to the regulator to adjust a resistor of some sort to regulate the field voltage on the rotor? One of the brushes seems to be connected to the B post, while the other seems to be connected to dead metal on the regulator, but there is a fair amount of resistance between the regulator metal and the alternator body (like 120Kohms). If the mechanism is that a voltage from the ECM tells the regulator to adjust that resistance, then the fact that I am seeing 12V coming up that line to A92 is concerning and makes me wonder if my remanufactured alternator has the wrong configuration of regulator.

At this point I will probably take out the reman alternator and look at the regulator to see if it is the same model as the original. I've seen stories elsewhere of remanufactured alternators having the wrong voltage regulator, so I am wondering if that is the story here.

If anyone has knowledge of how this regulator (Bosch F00M346098) should function, I'd love to learn. I know I can get a new regulator from FCP for about 50 bucks. If I find that the new alternator has the wrong regulator, I can order one...but apart from part number I'd like to know how I can tell that things are wrong.

 

During my lunchtime exploits, I verified that the new alternator has a working clutch as you describe The old one...not so much. However, I also verified that the drive gear is solid and not loose at all.

Is it possible that the bad clutch could ruin the alternator (electrically speaking) before it ruined the drive gear?

 

I took my lunch to pull the thing apart again. I managed to get the intake out in half an hour flat, very proud of myself.

I took some voltage measurements which were interesting. These are of course with the car on but not running (no intake manifold, after all)

Naturally the b-post was at the same as battery voltage around 12.2V (we're slightly discharged)

Pin 1 on the alternator was reading around 8V, while Pin 1 on the alternator connector was likewise reading around 8V.

Pin 2 on the alternator connector is not connected to anything and doesn't seem to have a purpose for existing.Pin 2 on the alternator itself also did not seem to show anything.

I decided to hook up the old alternator. Everything was the same except that pin 1 on the alternator was up at 11.5V.

This does not jibe with what I observed yesterday at the computer, but then again the computer may have behaved differently knowing that it was disconnected.

Comparing the two voltage regulators, the one on the remanufactured unit had a flimsier connector (could really move the connector around even when latched, even though it was a bear to get off). The original one is Bosch, the remanufactured one is some other brand marked made in Taiwan.

I decided to put the original regulator on the remanufactured alternator and see how it goes. It is still possible that the original regulator is what went bad in the first place, but I figure I can't hurt to try. Now that I know I can get the intake out in half an hour I feel like I can justify the time doing some testing.

I am finding it strange still that there are dueling voltages apparently colliding at pin 1 of the alternator. But perhaps the system is built to look at the differential (If my math and electronics are right, this means the computer should see 3.5 volts at A92. What that means...I have no idea. I guess we'll find out...

 

So I went down a LIN rabbit hole after doing some research on these voltage regulators. It seems they use a type of bi-directional serial communication, which explains why I see voltage both coming and going. So I was thinking perhaps the computer isn't bad after all...

And indeed, swapping the regulators did the trick! I got the car all back together and lo and behold, we're charging at a cool 13.5V - 14V!

So it seems that the new regulator which came with the remanufactured alternator is either bad or uses a newer version of the communication or just doesn't work for some other reason.

Of course, now I'm using the old regulator which has old brushes which is unfortunate, but I think that's an issue I can put off for another day. In the meantime, the darn thing works and I'm over the moon. And I'm now an expert in taking the intake off and putting it back on as an added bonus.

Thanks for being here for me to bounce stuff off of. I always think better when I can type out my thoughts. Hope everyone else is doing great!