I turn the potentiometer but the engine speed does not change, where should I start?
First look at whether the actuator moves; this splits the fault-finding in two. If the servo does not move at all, the supply and the potentiometer signal are to blame; if it moves but the speed does not change, the cable connection is. On the GS740-3P the yellow lead is the potentiometer wiper, the green lead is the potentiometer GND; red and black are the 12V/24V supply.
If the servo does not move at all:
- Is there voltage on the red (+) and black (GND) leads, and is the IP67 connector fully seated by turning?
- Does the voltage on the yellow (wiper) lead vary smoothly between 0 and 3.3V as the potentiometer is turned? If it stays fixed, the potentiometer or the cable is broken.
- If the green (pot GND) lead is not connected the signal is left without a reference; the measurement becomes meaningless.
- On the GS740-3P the memory may have been erased or the upper limit may never have been taught; carry out the calibration.
If the servo moves but the speed does not change:
- The cable may have slipped in the clamp or gone slack.
- If the cable sheath is not fixed at both ends the movement does not reach the throttle plate.
- The throttle lever may be mechanically seized or resting on the engine's own stop screw.
Also remember that on the GS740 a short press of the button switches between idle and working speed; while the system is in the idle position the potentiometer may appear to have no effect.
Full article: Electronic speed and throttle control on a diesel engine