Has anyone ever measured the voltage at the dp sensor with a voltmeter on the center signal wire?My machine has completely slowed down to a crawl on all functions but I can unplug the dp sensor and it speeds back up just like normal except the pump stays loaded up.I have all the manuals for it and I think the DP sensor is my problem.Key on engine off the sensor has 5 volts on the signal wire and with the machine running on I power it still has 5 volts all the time while working any function.The sensor voltage never changes from 5 volts under any condition.I dont have a scanner to actually read the DP pressure and just wonder could it be something other than the sensor causing this.I priced a sensor today through J.D. and it sells for $1060 so I really would like some input before I order it.
If you have the books check in operation and test, it shows which wires to test (2 and 3). Just back probe it with it connected as I assume you don't have the test harness. Its at the back of the book under differential pressure sensor voltage test and adjustment. It does sound like a failed dp sensor though. When you set it when you install the new one 0.2 volts will be really aggressive and 1.0 volts will be smoother 0.8 is where Id set it to start. P/N 4339559. I see some on ebay but I have never ordered one from china.
Andrew,Thats exactly how I checked my voltage.I dont have a test harness but I backprobed the right two wires just like the book said and still came up with 5 volts no matter what.My book is a genuine Deere book but it does not show anything about adjusting the DP sensor voltage when you install it.I have had mine out and noticed the nut on the end and thought it probably could be adjusted.Could you clarify?The p/n4339559 is what my J.D. dealer came up with also.I saw the sensors on E Bay but I am very leary of ordering from China.
Haley, What you are looking for is high voltage when the controls are in neutral and low voltage when you activate a function. Check voltage between the black wire and the center wire, usually white. There should be close to five volts between the two out side wires on the connector.
Sounds like its shorted to power internally. If it happened suddenly then I would assume that something is wrong with it, you could try adjusting it but I doubt it will help. To test and adjust key on eng off. To adjust, remove dp sensor, flip it over, loosen nut (13mm) adjust 4mm allen screw to voltage spec. Its in the hydraulic section under tests towards the back. If you have an early book it wont be there.
P.S. If you are not getting any fluctuation from the DP sensor you could swap it with the other DP sensor, they are the same. If you don't get a good reading from a know good sensor there could be a problem with the flow sensor valve. This is the valve that the DP sensor reads. It is basically a valve that creates a differential pressure between the pump input to that side of the valve and the return line to the tank to sense when a spool is opened and to measure the pressure that builds in the work port.
Andrew, My book does not show the sensor adjustment with the sensor out.What should the voltage be set on with key on engine off? It should be high or close to 5 volts right? I know how to adjust it but just dont have the voltage it should be adjusted to.Thanks for any info.
Jackdeere ,I dont think the 490E has two DP sensors.I wish I had a known good one to try but no such luck.Have you ever opened up the electrical end of one of these sensors? I wonder how it actually works and if mine could possibly fixed.I am exploring all options because I really dont want to spend over $1000 for a new sensor.
Supply voltage haley is 5vdc (pins 1+3) return from sensor on pin 2 should be .2-1vdc. pin 3 ground
you cannot fix the DP sensor. no other option but a new one.
DP sensor is adjustable not repairable.
I know its adjustable. try to use a dr zx. and you can see. its a big difference using a voltage tester and dr zx.
Manual specs using meter. Its pretty clear it needs changed and I doubt he happens to have mpdr or excavator diagnostics handy .
base on the symptom of what he is telling it needs replacement not calibration. In dr zx you can actually see the dp sensor data if its working or not. it hard to change it because of the $$$$ but thats the only solution you have. other option you can do is to borrow a good working DP sensor.
I think he already established that on around post one but again I doubt he has mpdr (drzx is an obsolete product and has been replaced with mpdr. Excavator diagnostics is the deere software) otherwise he probably wouldn't have posted this.
Andrew,Thanks for all your help.I have the 5 volts on pins 1&3 but pin 2 has a constant 5volts also all the time no matter what I do with the machine.I took the plug and screen out of the oil galley on my valve block,screwed the sensor back in and started the machine.When a function is moved there is a good stream of oil coming out of the plug hole so I think the oil supply to the sensor is good.I cut the top off of my sensor and there is more electronic stuff under ther than the law should allow(all sealed and non reparible).I am going to bite the bullet and order a sensor but still have a question about the sensor adjustment.The .2 -1volt on the return should be with key on engine off right?
Could anyone tell me where the dp sensor is located? I am having the same problem as far as my hydraulics being at a crawl. I have been concentrated on a fuel issue cause everytime I change filters and manually pump up the fuel system it runs great and hydraulics are fast but only for a min or 2 then right back to a crawl. I have replaced everything that is fuel related other than an injection pump.
On top of the control valve on the longer side.
Ok thank you I'm gonna go check it right now.
Well I bit the bullet and bought a new DP sensor.I installed it today and it fixed my problem.The new sensor was genuine Hitachi but it is non adjustable and a lot smaller on the electrical end than the old one was.Maybe this thread will help someone down the line with the same problem.
Glad to hear that!
I found this discussion searching the web for a problem I'm having with my Hitachi 120-2. I had this switch replaced in '15 or '16 and having the same symptoms again. I did order a $60 eBay one and it hasn't resolved my problem. My only test equipment is a Fluke multi meter. After seeing readings from both the old and new switch, I jumpered the +5vdc and white center wire and the engine loaded up and hydraulics were full power. When just watching readings, it looked like the voltage would vary while operating a hydraulic function and when needing full hydraulic power would need 5 volts but never got that high. My questions are doesn't it sound like I need the oem dp switch? and Has anyone had any luck with the fraction price aftermarket ones?