Need help understanding a Code

[wjcherokee]

My 2000 Wj through a code today and i dont know what it means, i would appreciate any help. I need to know what exactly it means and how to fix it.

Heres the code:

P1494 (M)
Leak Detection Pump Sw or Mechanical Fault
Incorrect input state detected for the Leak Detection Pump (LDP) pressure switch.

[JENSSEN]

 One thing to check  is vacuum leaks. Follow the small vacuum lines from the evap solenoid on the passenger side firewall back to the intake manifold. There is a rubber connector that hooks up to a fitting on the intake. Replace any soft, cracked or deteriorated lines. Make sure to check on the intake manifold under the throttlebody as vaccume lines can fall or come off and go unnoticed under there. There is also a  leak detection pump which is a little round thing near a green valve cover on the passenger fire wall; not sure if you can test it other than to swap it for a good know one.