My XC90 has a battery light that comes on now and then. I usually pull over, shut the car down and restart and I'm good to go. Only happens now and then and restarting the car puts the light out so I never really worried about it until my daughter took the car to school and broke down on her way home. Battery light came on and drained the battery. I dont think it is the alternator because when they stop charging they dont just start charging again..
I know these have an issue with the center bolt coming loose in the pully/gear. I dont think that is the issue with this but very well could be.

Wondering if anyone else has dealt with this issue or if anyone can steer me in the right direction.

Thank you

 

you need to measure the system voltage when the battery light comes on. don't rule out the alternator - it could be an intermittant fault in the voltage regulator or a problem with the connections/cabling. Also newer alternators have voltage sensing circuit to kick up the amps when needed so if that fails you can wind up running off the battery. I had a similar problem with my VW - battery light would come on, and a stop/start would reset. Put a meter on it and sure enough when the car was running I had 12.5V whenever the light was on, 14.5 when the light was off. VW recommended a new wire harness (said there was too much resistance (?) which took care of the problem all but once more so I'm thinking it was a connection to the the alternator.

 

There's no doubt the system is not charging when the light comes on. I have not been able to put a meter on it when the light is on as it happens so infrequently. I do have a midtronics tester. I went through the whole process. Battery, starting system, charging system with and without loads. All tests came back normal however, the light was not on. It very well could be the alternator but in my experience, when alternators are bad, they dont start to charge again. Just wondering if I'm overlooking something.
Thank you.

 

no I don't think you are overlooking anything. Intermittants are the hardest fault to trouble shoot, most people give up until they can produce the fault or randomly install replacement parts. About the only other thing I can think of is to check if there's any service bulletins or software updates available.

 

Thank you.

 

happened about 5 times this week while on the highway. Put it in neutral, turned the ignition off, started it back up and battery light goes out. Battery was new in October and terminals are clean.

 

Its happening pretty regularly now. 5 times on the way home from work. Ordered an alternator. Probably not the problem but I'll start there.

 

did u ever get an answer to this i was having the same issues and removed my alternator to get checked of course store cant check it cuz its special. I already have a new battery but it wont hold a charge at all i had to get it towed home. Now i have an alternator in hand that cant be tested and dont want to replace just to renove again.. any ideas?

 

Yes problem solved. It was the alternator. Do yourself a favor, get an OEM replacement. I purchased an new aftermarket replacement and it was not charging out of the box. I then bought a Bosch and that cured it. Not fun doing the job a second time! I still have the car today with no charging issues or battery light.
I'm betting a new or reman Bosch alternator will fix your problem.

 

+ on my post as well - I resolved my problem by replacing the alternator. Turns out there are relays in the voltage regulator that keep the alternator from overcharging the battery. In my case, the problem appeared after needing a jump start which was done with one of those portable devices - which I suspect fried the relay making it sticky. Unfortunately not all models allow you to replace the voltage regulator separately from the alternator so the whole unit got replaced.

 

Yup, same here.