Community Forums

Bigduke 60 · 05-21-2022, 06:46 PM

Can anyone help me find the terminating resistor on the engine end of a 2007 XC-R freightliner chassis W/ OM 926 la engine. I'm not getting any help at all from freightliner. I'm getting no resistance at all on the J 1939 data link. Thanks in advance.

Skip426 · 05-21-2022, 06:54 PM

If this resistor is at the engine end , have you talked to Cummins ?

Wiring harness on the engine is supplied by Cummins ,with the engine, and Freightliner chassis wiring just hooks to it.

gatorcq · 05-21-2022, 09:00 PM

silly question, normal resistors have the value stamp or color coded

Bigduke 60 · 05-21-2022, 09:06 PM

It's a Mercedes Benz engine OM 926 la. I was trying to locate it. it's on the engine side somewhere.

Bigduke 60 · 05-21-2022, 09:07 PM

I'm trying to locate it on the bus, it's on the engine side somewhere

n2zon · 05-22-2022, 06:49 PM

Quote:

Originally Posted by gatorcq

silly question, normal resistors have the value stamp or color coded

Yes, but finding it is sort of a prerequisite to reading its value.

FIRE UP · 05-23-2022, 11:56 PM

Bigduke,
I am no expert on this subject by any means but, I have dealt with the J-1939 data link a time or two in our coach. It's an '04 Itasca Horizon 36GD with the CAT C-7 330HP. In our Freightliner coach, that J-1939 Data link runs the full length of the coach. We have, like many, many Frieghtliner coaches of that era, have TWO diagnostic ports. One is at the very back of the coach, visible from the outside and just above the rear radiator. The second diagnostic port is up under the dash and can be a bear to locate.

Now, yes, there are TWO terminating resistors in the J-1939 Data link. There is one approximately 15" or so, from the rear diagnostic port. The data link consists of three wires. A yellow, and green and a black. There are multiple 3-way junction connectors all along the J-1939 main line. The terminating resistor at the end, near the rear on ours, is at the first 3-way junction and looks like a plugged end of the 3-way junction.

The second terminating resistor is built into what's called the *MMDC* on our coach. The MMDC is a Multi-Module-Data-Controller or, a small computer if you will. For some odd reason, Freightliner decided to put that $2 resistor inside a $450 component (MMDC) . If that $2 resistor goes bad, you have to replace the $450 computer or MMDC. Smart move Freightliner!!!!!!!!

Now, in my tests, between the C and D pins on the diagnostic port, I get very close to 59-60 ohms of resistance even though, each terminating resistor is 120 ohms each. I'm no electronic wiz kid by any means but, that's the reading I'm supposed to get. If the resistance goes to 120 ohms, then HOUSTON, WE HAVE A PROBLEM!!!!!!!!!!!!!

What that means when you get 120 ohms is:

1. One or the other terminating resistors is either malfunctioning or is missing
2. There is a broken connection in either the Yellow (+) or Green(-) wires in the J-1939 Data link.

If you're getting zero reading when testing for resistance in the J-1939 Data link, at the correct pins, I don't have a clue as to what your issue is. It would be interesting to hear what you find out.
Scott

Bigduke 60 · 05-24-2022, 10:21 PM

Fire up, Thank you very much. You are a very smart person. Everything you just told me it took me three weeks to find out. I talked with freightliner, they are telling me that second resistor is on top the motor. i didn't find it yet. The first one was under the dash. They said if both of those resistor is bad, or a broken wire at the connector. It would give me a 0 reading. I'm gonna keep on looking. i did find a bulkhead connector and a 3 way connector i wanna take a close look at for broken wires. Thanks again.

c_oneil · 05-25-2022, 08:03 AM

The "3 way connector" you say you found could be what you are looking for.
I don't have the same chassis as you but this is what my terminating resistors look like.

Bigduke 60 · 05-27-2022, 07:36 AM

C Oneil, Thank you very much. That's the one I found , it's made a little different, with a flange. I cleaned it up and now i'm getting 60 ohm of resistance on the J1939. I'm gonna hook everything back up and see if the check engine light goes out. Thanks again guys. ( my code is SPN 625 fmi 2 )

FIRE UP · 05-28-2022, 03:14 PM

Quote:

Originally Posted by Bigduke 60

C Oneil, Thank you very much. That's the one I found , it's made a little different, with a flange. I cleaned it up and now i'm getting 60 ohm of resistance on the J1939. I'm gonna hook everything back up and see if the check engine light goes out. Thanks again guys. ( my code is SPN 625 fmi 2 )

Yep,
60 ohms is what you're supposed to get on those checks. Hopefully, everything from this point on will be normal. Keep us informed will ya.
Scott

Bigduke 60 · 05-29-2022, 03:00 PM

Unfortunately, that's still not the problems. Hook the battery back up, check engine light still on. Same fault code SPN 625 fmi 2oc. It's unbelievable how hard it is to get this RV in a shop in Louisana or get someone to come check it out. All of the shops giving me the run around, and everyone who claim they can fix it, don't show up. I won't give up.