While I now have a 2008 my experience is with a 2002 but I think the operation is similar even thought the mechanics of the physical throttle pedal is different. In the throttle pedal there’s a switch which opens(or closes?) when you first move the pedal so there will be 2 wires to measure at the 23pin connector. @AssyRequired probably knows these pins. That switch is to let the controller know there’s throttle movement. Next, there is a variable resistor in the throttle switch with a voltage on one side of the resistor, ground on the other side of the resistor and the part which slides across the resistor and changes value as it slides(the wiper) is the 3rd connection.
I would think checking for the switch on/off action at the 23pin connector would be a good idea and then using the proper ground pin in the 23pin connector measure the voltage on the wiper pin while you move the throttle pedal.