What is meaning the DSA lamp when it is on? Does it mean the system is working or it is not?

Light on means it is not working. But that does not mean it's faulty, you may have accidentally turned it off. Here are some threads I will put is separate windows to make it easy to hyperlink: http://volvoforums.com/forum/volvo-s40-11/dsa-light-42738/

http://www.volvo-forums.com/t11258-dsa-light-on.htm http://www.volvoforums.org.uk/showthread.php?t=144192

http://esd.volvocars.com/site/owners-information/MY08/S40/S40_owners_manual_MY08_EN_tp9154web.pdf ..Page 131 BEST ONE

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