2005 Volvo s40 with a brand new battery and alternator
just bought the car and replaced both. Car runs just fine
ac-heat doesn’t blow
radio works and car doesn’t die. I have no issues at all besides the power system service urgent warning and battery light
charging system holds just fine, battery doesn’t drain
car has 109k miles
not sure where to start

 

Where did you get the alternator you put in?

 

a shop installed it. But the old alternator was overcharging and putting out 16 volts. This one is working. The previous owner had the old alternator rebuilt and it didn’t work

 

Older alternator circuits were simple. If the charging voltage was higher than the battery voltage - the light went out on the dash. The one small wire on the alternator went directly to one side of that dash bulb, and the big wire goes to the battery. .

That small wire now (in your car) carries a LIN (local interconnect network) signal. That signal goes to the Engine control module (both turbo and non- turbo ECM's are shown on the diagrams, there's not 2 ECM's in your car), is processed and sent to the CEM and DIM (dash cluster) over the CANBUS. (in the diagrams 6/26 is the alternator)

7/3 is the battery temp sensor - connected to the CEM. So the CEM can control the charging rate depending on the battery temp. (by talking over the CANBUS to the to the ECM if needed)

I'd bet your shop installed the wrong alternator. Yes it charges but is not sending the correct signal, or may not have have the ability to send the correct signal over the LIN, probably due to the voltage regulator in the alternator.

 

When I inherited my late brothers S40 2.4 it had the same problem , was a incorrect alternator , as mentioned the best bet is to get one from the agents , expensive but will save you a lot of hassles , however this was like 10 years ago so now the value of the car is much less so perhaps a clever electronic chap can help

 

Where did you get the alternator you put in?