Hi everyone. First time here, just looking after a 1999 S40 1.9 Diesel for a friend, and got an annoying intermittent issue....

It starts with a red flashing door symbol light on the dash. It doesn't flash normally, more fades on and then fades out repeatedly. When this happens the following things occur.....

a) Interior courtesy lights stop working
b) Stereo won't power up.
c) Central locking from inside the car (using the dash button) will work a couple of times and then fail.
d) Exterior locking of doors does not activate central locking
e) Alarm will not activate either through key
f) Remote central locking via the key fob, stops working.

If I disconnect the battery, everything will return to normal for a while, but then the door symbol on the dash starts fading in and out again and all the above symptoms all re-occur at the same time.

Not sure if it's related but indicators will also fail intermittently at separate times, and on the dash, the right hand turn indicator sometimes works and sometimes doesn't, regardless if the indicators are actually working.

Any ideas? Help?

 

First suspect is low voltage from the battery. Are the cables clean, battery good, etc?

Second is backfeed from a blown fuse. My 2005 had some very strange interior lighting issues that I finally fixed upon replacing a blown fuse. The bad fuse was not marked for interior lights though which is why I missed it for so long. Out of desperation I pulled every single fuse until I found the bad one.

Third suspect would be the Central Electronic Module (CEM). This module is the bad actor when one headlight mysteriously won't work on low beams even when the bulb is good.