Gehl rt175 ecm communication

[rmllarue91]

Yanmar 4tnv98 znms ecm is pulling down can a and b communication lines checked harnesses and unplugged all electronic components still pulling can down. With ecm unhooked other controllers work but engine won't run. So I cut one can line and it runs and operates but shows codes for no com with engine controller. Anyone ran into similar issue with ecm failing on can lines? Thanks hef

 

[Txhayseed]

You checked the CAN lines ? Are you saying you checked can hi and can low ??? Then you cut either can hi or can low ??? And now have an ecu communication error ? Well i think that answers your own question as to ecm com errors. Am i understanding you correctly ? What do you mean pulling down like the battery is going dead ? If i am reading that right how did you test can hi and can low to determine you needed to cut wires ? The Only way to test and can hi/ can low is with an oscilloscope. Thats it, hands down, regardless of what people say a volt meter is worthless and will give you nothing but a rabbit hole to go down. On CAN systems you cant just unplug things randomly for testing and hope to stumble upon the issue thats just not how the systems work. Definitely wouldn't start cutting wires on a hunch especially my high speed high priority wires. Still unclear on ecm is pulling down. Can you go into more detials ?

 

[Midnightmoon]

Check resistance between can hi and can low key off all controllers hooked up at diagnostic port yellow wire is hi green is low. Check resistance from can hi to ground. Check resistance can lo to ground. Key on check voltage at can high should be above 2.5volts check can low voltage should be below 2.5volts. What were the original codes you had before you started working on the machine?

 

[rmllarue91]

Hey tx and midnight
Original complaint console monitor shows codes for each off 4 other modules no communication.
1-2
1-3
1-4
1-5
I checked voltage on can high low both .1ish if a volt.
Then I check powers and grounds to all modules ( verified voltage and load tested each)
Then I unhooked modules one at a time till network came back ( ecm )
With ecm unplugged console module talked to others allowing safety's and controls to work.
But did display 1-2 ecm com and code 27 also related to ecm com.
So I totally unhooked everything everything on engine and related to ecm plugged ecm back in and still pulls can lines down..... Looking like bad ecm.

 

[rmllarue91]

Volts with network working was around 2.5 on each but i didn't make note.


with it acting up .1 or .2 volts on either.
( Ecm plugged in )
I was ready to call faulty ecm
Owner says if you jump starter relay it starts and runs... I verified.
This is when I figured ecm didn't need can to operate just to display info on console. ( Injection pump needs ecm to run )

So I cut one can wire at ecm ( don't remember which one ) and machine runs and operates and I only have codes for communication with ecm not whole machine. 1-2

So only fault is ecm has issue on can circuit. ( Can't figure away to isolate it more)

I don't have scan tool for machine
( With no com probably don't matter )
I don't have a scope yet
Customer may have jump started with 24v power source.....
I'm pretty confident in bad ecm unless someone has other ideas of what to check

 

[Midnightmoon]

Its important to verify the resistance between can high and low are correct. with everything connected you should have 60ohms. if you have 120 one resistor is bad. if you have 0 both resistors are bad. This could be caused by the harness or controller. If you have 120 with everything connected and unplug the ecu and still have 120 then the resistor in the ecu is bad. It sounds like the ecu is shorting out can high and low. check resistance of can pins on ecu to all other pins and to ground to confirm bad ecu. Also with harness disconnected check resistance of can high and low to all the other pins in the harness and to ground. if you have resistance in harness but not ecu you have a short in the harness. What can wire did you cut? it sounds like you may have a short in the harness.

 

[Midnightmoon]

After re reading this am I correct in saying customer may have jump started with 24 volts and now it wont start? If thats the case and it will run if you jump starter relay you may just have a bad fuse or relay. I had one of these that had a starting issue and it was just a bad relay.

 

[Txhayseed]

Your are correct can is not needed to start. You can still jump start by going old school but you need can communication on the bus for everything else to send and receive. You can test as mentioned with a meter but just take into account your testing to make sure both resistors are good and your ohm'n out pin to pin. You still wont have any idea where can hi and can low are in there respective cycle or how clean your can signal is. You can have voltages that are respective to the outputs but still have a very rough can wave.

 

[rmllarue91]

I did ohm harnesses and cross check for shorts harness tests fine
I didn't ohm resistors ( thought of it after I left )
with system all hooked up it won't start with can system down because of crank interlock. With ecm unhooked it will crank but won't start with ecm unhooked

 

[rmllarue91]

Next move is to ohm can high and low pins on ecm
ONLY ISSUE IS CAN LINES DOWN
I don't recall which line I cut
I agree scope would help but this is and ( on or off ) issue not slight or intermittent
I wonder if 24v could have damaged resistors in ecm ( ohm test will tell me ) thanks for help so far guys the comments really get me thinking

 

[mg2361]

I know nothing about your machine, however if I am not mistaken, all controllers have a "CAN" transceiver in them (they call each controller a node) and you can test the transceiver with an ohmmeter. Not always 100% accurate but I have nailed down drops in CAN voltage with this test. With the controller unplugged and not powered up measure the resistance as seen below.

 

[rmllarue91]

Ive been to this customers few times working on other stuff but haven't had a chance to ohm that controller and it pisses me off lol but he's been using it for over a month with machine not communicating with engine controller....