Fault 26 Electronic throttle sticking.
Fault 27 Throttle position sensor value differs from SECM calculation
Fault 28 ETC spring or same as 26.
Above faults are frequently associated with throttle body open wiring
First check the wiring and plugs to and from throttle pedal.

Check for opens or disconnect on throttle body plug area.
Doosan's often have broken wiring where the harness connects to
the throttle body plug. Occasionally when running if the wires are
manipulated engine speed will change indicating an open.