Hitachi ex 120-3 hydraulic problems

Been looking at problems with the hydraulic system on excavator.
Unit is making the pump go to full stroke and will stall out the motor when commanding any functions. Unit smokes hard as well and will not recover unless you stop using any functions. Have checked out the fuel system and changed fuel filters and cleaned the screen in the banjo fitting. Have also checked the turbo and the air filter and inlet hose from the air filter to turbo. Have checked all the fuses and made sure the computers are flashing the red light as well. Have also check the the 2 solenoids on the pump for ohms of resistance and for power as well. Both solenoids have power when unit is first fired up when cold but as unit warms up the pump will start to stroke up and loses power to the solenoids. Checked the wiring back to the relay in the cab that supply’s the power and the computer is shutting off the ground to the relay when this happens. So I’m at a loss of where to look now. Is there a way to check codes on the machine with out at code reader like flash codes or any thing that way
Thanks Frere

Welcome to HEF Frere!

There should be a 4 pin connector I think is behind your right arm rest. Looking into the connector with the lock tab up, short the two terminals on the right. Key on and watch the blinking light on the bottom controller for codes.

Thanks I will try that and see what flash codes it shows then

Went out to unit and pulled flash codes 29 and 30 which is to do with the angle sensor on the pump. Checked voltage to the sensor and the the ground both test good.
Ordering new sensor for unit.
When replacing the sensor is there away to set the sensor with out having a the computer to check it. Can it be done with a voltmeter?

Make sure if you replace that sensor as to not lose that little spring on the end of the shaft. Punch mark on the shaft is mounted opposite the wire harness side. To adjust it, have the hydraulics warmed up, engine idling, unplug both pump solenoids, wait about five minutes, then adjust the angle sensor to read 4.40 - 4.45 volts (you will have to backprobe the sense wire carefully to measure that).

Thanks for the info will give that a try when I get new sensor

Well got new sensor and installed it on unit set it up to 4.45 bolts on the sensor return and plugged to 2 solenoids back in and shut unit down and unhooked the battery’s to clear codes and fired unit back up and unit is still in full stroke on the pumps. Left the voltmeter hooked up to the A sensor return wire and the run the functions and the swash plate is not moving. Shut unit down and checked the flash codes and it has code 22 and code 29. Went through and unhooked pvc controller and ohm out all wires to the a sensor and the dp sensor and the p sensor and the n sensor to the ecv controller and the 2 solenoids on the pump to the pcv and the relay as well. Checked all grounds and power supply to the ecv and the pcv and all tests good. Hooked all stuff back up and fired unit up with ohm meter hooked up the the a sensor return and it started out at about 1.75 bolts and slowly started to climb the voltage and slowly started to load the motor more and more till the pump was at full stroke and would stall the motor out if trying any function. So it still show code 22 and 29 after it goes to full stroke on the pumps. So I don’t know what to test or change next. I bought new a sensor from hitachi. Was also going to check the pilot pressure when I get the proper fitting as well. Thanks for the help

22 - Pump Control not normal
29 - Short circuit of angle sensor or the wiring harness.

When you checked the wires to the A sensor did you check all the wires for continuity to ground? Continuity to other wires?

If the PVC detects any issues which it is clearly showing, then it removes the ground from the pump control relay.

Well I went out and checked all the wiring again and now I cannot find continuity to the 5 volt supply wire to the A sensor from the computer. Some how I missed that but I still have 5 volts to the a sensor so I must have a wiring problem or are all 3 sensors the (dp,A, and p sensors) use the same 5 volt source.
Would some one have a wiring harness diagram as the one I have I found on line and cannot read it very well as it is poor picture and when you zoom in can’t read any of the wire colours or PIN number in the pcv connector

I PM'd you.

Well got unit fixed. Found out all the wiring was good. Was out of ideas on how to fix as unit would still not function and was still throwing code 22 and 29. So I drained the oil and installed pressure gauge in the pressure port for the pilot pressure. I also removed both solenoid valves for the pump control of the swash. Before taking the valves apart I tested with air and they where both passing a lot of air. Filled them with oil and tested again and found that they would pass air and oil as well. Took the valves apart and found that all the orings where cooked. Replaced all the orings and checked the screens and put back together. Tested both valves with air and oiled up and no leaks. Install the valves on the pump and filled with and fired unit. Found the pilot pressure was good and then notice that the pressure surge was back on the pilot line and could hear the solenoids clicking on the pump again. Tested unit with owner and he said that is best it has worked since he owned it.
So the A sensor was bad in the end result and the orings on the solenoid valves where cooked and bypassing oil.
Thanks for all the help Frere