Outer Limits 4x4 Board

hey guys one of mine has gone and wondering if they go often i bought mine 2nd hand but it only has 37000klm on the clock. 230 for the sensor and 80 bucks to install it... i know its an easy job but they reckon cause there is two they have to go thru some charts to see which one it is...
is my only option holden or can i get them from somewhere else and work out which one it is...
thanks
jason