Good to know that both of you have these cars and keeping them running.
The engine and transmission are bullet proof.
Some of the stuff mounted on the engine will wear out due to age etc.
Fuel pressure regulator diaphragm will tear and pump raw gas into the intake.
It will not code or run rough. Remove vacuum hose from regulator. Bump the starter.
If gas pours out of pressure regulator, replace pressure regulator.
Idle valve S hose will crack due to age and hose drying out and engine shake.
This will cause a start/die event. Inspect, replace S hose if it is old and worn out.
I do not have an answer for the alternator issue.
Volvo wiring starting/charging for S40 2000-2004 is not that clear.
There are 2 different engine management systems.
EMS 2000 and Melco 1 or 2.
US market has EMS 2000 only.
Below pic shows the CEM, it should be 4/38 not 4/56 controlling alternator charging.
Each charging wiring diagram for 2000, 2001, 2002, 2004 show green circle X out Melco charging
that we do not have for the US market.
2003 charging diagram shows the below pic only.
I am guessing that all 2000-2004 should have the charging controlled by the CEM.
I could be wrong and yes you do have the green circle charging system.
CEM controls lots of stuff.
One issue was one headlight left or right would not turn on.
We would have cars come in from indie repair shops that replaced the headlight assembly and still not turn on. Replacing the CEM fixed it. Tail lights would be dead, CEM fixed it.
We all kept a used CEM in out tool box for testing. We would write on the case what light, function did not work. When we got a system down, we would look at the saved used CEM’s for a working system for testing. I do not remember any CEM having an issue for not charging.
CEM’s are plug and play, no software. Below are CEM p/n’s and VIN range.
28 Control unit 1.00 30896697 CH -799999 (-2001), L.H.D Central electronic module (CEM).
Electronics box 1.00 30638707 CH 800000-999999 (2003), CH 1- (2003-), L.H.D
Central electronic module (CEM).
Control unit 1.00 30896698 CH -799999 (-2001), R.H.D
Central electronic module (CEM). Electronics box 1.00 30638708
CH 800000-999999 (2003), CH 1- (2003-), R.H.D Central electronic module (CEM).
Xemodex has a repair service for this CEM. They do not mention any symptoms or issues.
Call and talk to Xemodex about this. They are very helpful over the phone.
Xemodex Inc Technology Improved United States | 1-888-712-2525
Central Electronic Module Repair For Volvo S40,V40 | XeMODeX Inc.