This is the Case Fan Pinout for the Proliant ML310 Generation 1, may be compatible to other Proliant Servers and ML310 Generations.
Uses non-standard 5-Pin-Fan-Connector, possibly to lock out cheap 3rd party fans.
The only special lines are the "Status"-Line and the 5th Pin. For normal operation, Status (Pin 2) is tied to Pin 1 (GND). An Open Pin 2 means either "Fan not present" or "Fan Failure". The 5th Pin may be a PWM-Control Signal for the Fan, but it is not necessary to connect it.
|Description (may be empty)|
|2||Status||Fan Present / Fan Failure|
|4||Sense||Standard Tachometry Signal|
|5||? PWM||possibly PWM-Control Signal, optional|
Bridge Pin 1 and 2 to be able to connect normal Fans.
5pin CPU connectors letting pin 5 open. System complains on boot: Fan solution not sufficient. This means, that pin 5 has to be connected, but I it is not known what has to be connected there.