Hi Craig, The 20% to 80% is what you should be getting ,however I don't understand why the duty cycle does not change when you release the park brake, unless there is some issue with the wiring .Have you checked the harness from the joystick to the ECM?
The output from the joystick is only a proportional signal to the ECM which then controls the functions.
As stated earlier the Aux ECM has been known to be problematic
Cat ET is probably your best bet at this time
here is a fault light chart that may help
The output from the joystick is only a proportional signal to the ECM which then controls the functions.
As stated earlier the Aux ECM has been known to be problematic
Cat ET is probably your best bet at this time
here is a fault light chart that may help