JD 490E computer problem?

dirt MD · Mar 29, 2021

Hello there.
just bought a 1995 Deere 490E from nephew of a guy that died of COVID so don't know much about the machine.
nephew is telling me it needs a "hydraulic computer"

behind the seat there are two computers.
the computer on "top" is blinking, sequence is ...5235734523573... which just repeats (don't know which number is first)

the "lower computer" there are no lights blinking. because he told me the bottom computer was the fault, I purchased and replaced but still the same problem... and new computer (bottom computer) still no lights.
--> starts and runs fine, can crawl, but engine stalls when using boom, stick, bucket, unless its in "P" mode and even then it stalls especially with the stick outstretched at all and moving bucket..

not sure which computer is which, but is the problem with the top computer given that it is flashing?
any resources on any of this anyone knows about or where to start to try to diagnose this ?

thanks !!

mg2361 · Mar 30, 2021

Welcome to HEF dirt

!

Ignore the top controller. No lights at all on the bottom controller?

If no light comes on on the PVC (bottom controller) then there is a power issue, ground issue, or a short in the wiring shutting down the controller. All the fuses good, especially the F7 1 amp Valve Controller fuse? Also check the F4 1 amp PVC Backup fuse.

dirt MD · Apr 3, 2021

Thanks so much for your welcome mg!

I am reading zero on F4
And 120mV on F7

does the backup need voltage?
Thanks!!

mg2361 · Apr 4, 2021

dirt MD said:
I am reading zero on F4
And 120mV on F7

You measured both sides of the fuses with the key on and have no voltage? They should both have battery voltage through them with the key on. You would need to find out why. Do you have voltage on both sides of the F8 and 9 fuses?

dirt MD · Apr 4, 2021

I feel like we are getting somewhere, I so appreciate your advice !

following are voltages at the fusebox :

1. 6mV
2. 10mV
3. 26mV
4. 0
5. 21mV
6. 2.3mV
7. 121 mV
8. 0
9. 0
10. empty
11. 0
12. 0
13. 0
14. 0
15. 0
16. 0
17. 0
18. empty
19. 0
20. empty

I am measuring voltage through the fuse. should i measure each side individually ?

thanks again !!

mg2361 · Apr 5, 2021

dirt MD said:
I am measuring voltage through the fuse. should i measure each side individually ?

Yes. Ground your meter to a good ground and measure the voltage on both sides of the fuse with your red lead. Just do the fuses I mentioned.

dirt MD · Apr 10, 2021

Hi Mg

sorry I was mixed up.
I retested with the directions you indicated above (using red lead on each side of the fuse, connected to good ground.
and all fuses tested had 23-24 volts on both sides (including F8 and 9 fuses)

mg2361 · Apr 11, 2021

Now you have 2 choices. If you have the operation and test manual, you can locate and test voltage supply at the PVC as well as test the grounds for the PVC. Another thing you can do is with the key off unplug all your sensors (there are quite a few). With them all unplugged, turn your key to the on position. Does the light on the PVC flash? If it does then there is a bad sensor causing it. Plug the sensors back in one at a time until the light goes solid or goes out. That would be your problem sensor.

If the light does not come on with the sensors unplugged this one could be a little tougher to solve. It would mean you have a short in the wiring harness or a faulty PVC. I have a home made wiring setup that I use to bench test the controllers to eliminate the wiring. I supply voltage and grounds to the appropriate pins to see if the controller light starts blinking. You have to be careful with this as to not short any terminals that won't be happy

having voltage to them. Below is not from a 490E, but from a newer Deere/Hitachi machine as an example.

LACHAU · Apr 12, 2021

mg2361 said:
Now you have 2 choices. If you have the operation and test manual, you can locate and test voltage supply at the PVC as well as test the grounds for the PVC. Another thing you can do is with the key off unplug all your sensors (there are quite a few). With them all unplugged, turn your key to the on position. Does the light on the PVC flash? If it does then there is a bad sensor causing it. Plug the sensors back in one at a time until the light goes solid or goes out. That would be your problem sensor.

If the light does not come on with the sensors unplugged this one could be a little tougher to solve. It would mean you have a short in the wiring harness or a faulty PVC. I have a home made wiring setup that I use to bench test the controllers to eliminate the wiring. I supply voltage and grounds to the appropriate pins to see if the controller light starts blinking. You have to be careful with this as to not short any terminals that won't be happy having voltage to them. Below is not from a 490E, but from a newer Deere/Hitachi machine as an example.

View attachment 237221

Great idea.

dirt MD · Apr 17, 2021

Attatched is the schematic from my operation and test manual for those who may run into this problem in the future.

I have tried replacing the PVC already which unfortunately did not solve the problem. I am thinking your suspicion of sensor could be possible. Which sensors interface with PVC that should be disconnected?

dirt MD · Apr 17, 2021

oops here is the schematic

mg2361 · Apr 18, 2021

dirt MD said:
Which sensors interface with PVC that should be disconnected?

I would do sensors AND solenoids. See below.

Egetebee · Apr 18, 2021

Hiya Dirtmd,
I have a Hitachi EX120 and my understanding is that the JD490E is nearly an identical machine. Regarding the fuse panel behind the seat, the inside rail is the source power while the outside rail is to the accessory itself, so measuring voltage on each side of the fuse helps determine both source power & the fuse itself.

I also had 0 volts on fuses 6-13 which turned out to be a 'fuse' type thing in the battery bay and just solved the problem of which mg2361 (& others) was a tremendous help, so you're in good hands.

Just in case it's somehow related here's a link to my issue
EG

dirt MD · Apr 18, 2021

Good hands indeed! - let there be light!
Mg is a wizard! ‍♂️

Per your instructions I went through the sensors one by one.

I have disconnected what I *think is the engine control motor relay??

I lost the lower panel below the hydraulic access where the engine control motor is located. Previous owner spliced these incorrectly.

I disconnected the wires and now the PVC is blinking !

machine runs WAY better now. But I still have the relay disconnected- is this dangerous to run in this manner ?
Thanks so much !!

mg2361 · Apr 19, 2021

dirt MD said:
what I *think is the engine control motor relay??

At Deere we call it an EC (engine control) Motor.

Does the engine run at a constant 1800 rpm? That's not good to be starting and stopping an engine at those rpms.

JD 490E computer problem?

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