working on a hitachi 120-2 grey market machine.. first had issue with the stop motor, fixed bad wiring and bad motor and now that works properly. The e.c. motor was replaced before I had my hands on the machine. When I started my diagnosis It would start in the "p" selection but die when I selected idle button. I started testing the e.c. motor relay and I had a little over 1 volts at the number 2 leg of the relay and in the book it says there should be no power here and if there is then to test the output side of the switch of said circut to eliminate bad harness issues and if its the same they say its the controller issue (EC). After I pulled the relay out inspected and reinstalled I now have 24v on the same leg and the motor will now not function at all. It also says in the book that the switch for that circut is in the pump valve controller (pvc) pin #104 and to use the key switch to test the switch. When I test the switch using the key it goes from 24v key off to 1.5v key on. Should this be switching the circut to ground key on? Also before I checked the relay I took a video of the e.c. motor to see if it would move the control arm without being hooked to the cable and it didn't move much at all and makes a loud growling noise and acted like the gears in the motor were stripped but the gears are fine so I figured it had to be a control issue. Any help is much appreciated
Welcome to HEF roser21 ! Pin 2 of the EC motor relay will have 24V with the key off because the controller is not supplying a ground (pin 1 comes direct from the battery through a F3 fuse). With the key on the controller can supply a ground and therefore the drop in voltage. With the key off disconnect the EC motor ( do NOT disconnect/connect the EC motor with the key on, you will ruin the Engine controller ). Turn key on and measure the voltage at the 4 pins of the EC motor connector. Key off, reconnect. Turn key on (engine off) and set to low idle. Backprobe the 4 wires and measure the voltages. Report your findings. Hopefully Lachau sees this and can respond. He is the man for Hitachi info !
I really have confused when I read your post!!! Hitachi EX120-2 excavator has 02 controller: 1/- PVC = P ump V alve C ontroller and 2/- EC = E ngine C ontroller Your malfunction is "THROTTLE CONTROL" which means it's EC related, not PVC . You have tested PVC instead of EC checking??!! I suspect that you have wrongly checked the relay, instead of checking the EC motor relay you have gone to check Pump control relay??!!
Sorry for the confusion. It was confusing to me as well. In the book it says to test the switch that controls the e.c. motor by testing pin 104 on the pvc connector. It says if you have more than 0 volts the e.c. is the problem. I replaced the computer (EC) and this took care of the problem. The e.c. motor sounded awful. Made growling noise and would move hardly any. Also towards the end of my diagnosis it lost its ability to even provide a ground for the motor. Thanks for all the help everyone