Dell PowerEdge Fans runs always in full speed

Hi

I have a problem witht one Dell Poweredge 2900 server. The server always runs the fans in full rpm.

I tried to update the latest bios and the ESM firmware, but the problem is not solved.

The Dell OpenManage displays only one error, the chassis intrusion says, case is open, but the case is closed correctly. I think the sensor is bad, I try to search the switch but i can't find it.

Please let me know where is the chassis intrusion switch on this server, or how to disable it.

Thanks