Getting too much information / input is worse than not getting enough . Opinions are the same .
The battery replacement is ( according to the readings shown ) looks like a good idea . The alternator ripple 0.60 or 600 mv is high . I don't remember how much is allowable . That is the result of bad diodes inside the alternator . A.C. v in the D.C. system can cause all kinds of problems .
Good luck !

 

I wouldn't put much stock in the "factory trained" guy who said to keep the plugs in for 150,000 miles.

Which update was from the dealer?

 

the dealer basically said I need a new cat for $3200, they didn't come across all the same problems that the independent shop guy did. I was having a problem where my heater would surge & blow cold air for a few seconds every minute or so, since changing the battery, It hasnt done that - so it leads me to believe that the battery was causing some odd codes. I drove for 80-90 miles today and the code came back for the cat. Thinking about spacers but should I be worried about potentially ignoring a big problem? The notes from the dealership regarding the cat is: diagnostic tests found rear oxygen sensor on bank 2 tracking with front sensor. Indication of a failed catalytic converter" they said I also have a small oil leak but they didn't investigate to see where it was coming from because that would be another $120 & I was short on time.

 

Can you say that last part in English?

 

Alternating current voltage in a direct current voltage ( automotive electrical system ) setting will cause all kinds of problems . The printout reading showed 600 millivolt A.C. voltage and I think 300 millivolt is about as much as you want.
I hope this helps .

 

yes, it does, but I guess what I'm wondering is what I should/could do about the high number?

 

I've replaced a couple of cats on v8 before.

 

Please let me know any information you have that could be beneficial!

 

Unless there's something I don't know - and there may be - about installing a catalytic converter on an XC90, that's a crazy price.

As far as I can tell the Volvo part number for the cat for your vehicle (2.5T) is 8603848. Google that part number and you can see the discounted price for a genuine Volvo part is about $1,100 versus about $1,300 at the dealer.

If you eventually decide you need a new cat try and find a friendly muffler shop - use Yelp - who will install your Volvo part.

 

It's a V8, not 2.5T.

 

Two banks of O2 sensors, OK.

OP, just checked Rockauto for your cat and here's an interesting option. Davico Mfg. makes aftermarket cats and needs a first piece prototype for the V8 XC90. Looks like they would build you a cat for $171 if you send them your current cat 100% intact. This may be too difficult for you but I might try it if this were my car.

 

alternator needs to be replaced . The part(s) that are bad are inside the alternator.
You need to replace it w / a quality part . If there are alternator rebuilders in your town or area consult them for pricing . Check automotive parts vendors on prices and warranty .
I don't know about your / your spouse's mechanical ability. That will be your decision . If you think you can DIY . go ahead !

 

Don't assume your alternator is toast. 0.5V AC is the upper limit as a rule of thumb but normally operating heavy duty alternators can produce more ripple - up to 1.0V. The ripple voltage is also influenced by how it's measured.

I'd put this on the back burner for now. Maybe seek out a specialist alternator repair shop and take your car there for a proper diagnosis when you have time. It would be better to have your Volvo alternator repaired if it needs it than to install a cheap aftermarket alternator.

 

I do not believe your alternator is the problem here. Though they are common to fail on the V8. They always (in all cases I've seen) set a Power System Service Required warning though for under/over charging.

 

UPDATE:
Just went & had the codes pulled down the street since we hadn't since it first came on 2 days ago (Sunday morning). I was surprised to see misfire codes in cylinder 2, 3, 4 & 7 - any particular reason why it would be those cylinders? It also had the P0300 code.
Also, I have not felt any loss of power or had a flashing CEL at all, which I did the other times that I had misfires. We are looking at the spark plugs this week, but would that cause the random misfires? No other codes by the way, no sensors or anything like that this time.

 

In other words all you've done so far is install a new battery.

Change the plugs.

So you're the fleet manager. What does your husband contribute?

 

Basically he's not happy that the car I bought is so troublesome so he's left it for me to figure out. I bought him a spark plug socket today so he'd take them out, but he really knows nothing about cars so he didn't do anything.

Yes, battery change & air filter change. I was trying to avoid having to pay someone to change the spark plugs, but it doesn't look like that's going to happen. A lot of people sounded like they thought the misfires could be helped by the battery, so I just wanted to add in that it they are still there.

 

Ive never seen a battery cause a misfire. You will also need a tool to disconnect the fuel like to get the back 4 plugs.

 

Step 1 for a misfire on an engine overdue for spark plugs is to replace the spark plugs, never a battery.

 

I must have misunderstood, I thought since almost everything is computer run, that the low battery could make it misfire based on things not being timed right. But yes, spark plugs are next on the list!