O.k the name "Dawes" valve came from a bloke in the U.S, Darren Dawes, who invented this wonderfull little valve for VNT, or vacuum operated turbo's. In a nutshell, what this valve does is take away the ECU's ability to control the boost levels. The ECU in your Patrol isn't very smart at controlling boost levels, and therefor you would experience limp mode.
So the Dawes valve is a little mechanical valve which is installed in the vacuum system on the engine and you say bye bye to the ecu's control. But, you need a boost gauge installed first before the Dawes is installed so you know what pressure to set the Dawes at.
The Dawes valve can be installed on just about any vacuum operated turbo, Patrols, VW's and Tritons, to have the final say on how much boost you want.
Cheers.