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Old 01-26-2023, 11:26 AM   #1
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Losing signal from ecm

2004 journeyóFreightliner chassis 330 cat. Started out losing cruise control intermittently, then speedometer quit for a few minutes, then all the dash gauges stopped registering. This all happened over a period of 100 miles. Every time I would hit a little bump or bridge approach everything would come back for a short period of time then Iíd lose it again. Check engine light on abs light on. Message center says no input from ECM. Freightliner spent a couple hours looking for the obvious but came up short. Just wondering if anyone else ever had this happen before I spend a fortune trying to figure this out. Thank you in advance
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Old 01-26-2023, 12:27 PM   #2
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Always start out with basics. Power that feeds chassis distribution center and grounds all chassis grounds. A lot of MHs have 10ga power wire feeds the dash and trans pad with inline fuse within 18" or so.Its battery loop connection and inline fuse holder have given owners trouble.
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Old 01-26-2023, 03:40 PM   #3
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Check main ground cable connection(s) from chassis batteries to frame rail or starter bolted to frame rail for lose or corroded connection.
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Old 01-28-2023, 09:47 AM   #4
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An 04 coach maybe on an 03 Freightliner chassis and be in the middle of a wiring and gauge package change on Freightliner chassis .

Does your gauge package include this display module ?
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Old 02-01-2023, 09:50 AM   #5
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Quote:
Originally Posted by Skip426 View Post
An 04 coach maybe on an 03 Freightliner chassis and be in the middle of a wiring and gauge package change on Freightliner chassis .



Does your gauge package include this display module ?


Hey skipóóso sorry about taking so long to respond. Have not been able to log in for some reason and had to get help. I ran the vin number on my chassis and it comes up as 2004. I have the message center but I think itís a little different cause Iíve never seen the Freightliner logo. Have had this coach for 6 years and put 35k miles on it. Only other issue Iíve had with the dash is every so often the idiot lights would go through like a test mode out of the blue and consecutively light up very fast, like two seconds, and run this pattern for a couple dozen times and then settle in back to normal. Wouldnít affect anything, just kind of weird on the randomness. My coach is at Freightliner in Columbus Ohio where I left it when the fan hub went out on me. This issue with the dash just happened to rear I itís head the same day. Couple of days before the speedometer quit and had check engine and ABís light on for about five minutes then everything went back to normal. But this time everything electrical in the dash,abs,check engine lights were back and forth for over a hundred miles. Freightliner was able to duplicate the issue, but after 8 hours labor at 220 an hour were unable to find the source. The slightest bump in the road would cause the problem. I would think a shop would have the tools to locate a short but then again maybe Iím wrong. Told them they could have one more day and havenít heard back yet. By the wayó-took over two months to procure the parts to rebuild the fan hub. Unreal. Glad I had the Jeep and just went home but on the other hand being 500 miles away from your coach doesnít give a guy much leverage.
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Old 02-03-2023, 08:45 AM   #6
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ground connections where the gauges are
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Old 02-03-2023, 12:19 PM   #7
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I had the same problem on my 04 chassis. My solution turned out to be the harness plugs on the MMDC control module. The module is located in the front drivers side compartment where all the fuses and electircal components are located. There are two connectors, a wide one and a narrow one. I had to remove the connectors, clean the pins and sockets with contact cleaner and small brush [tooth brush], coat with dieelectric grease and replug making sure not to damage the pins. I have not had an issue since.
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Old 02-04-2023, 07:25 PM   #8
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Ronnie, has touched on a possible cause of your issue ; which is an intermittent open circuit , not a short.

Shorts , burn out fuses and wiring .

Open circuits , are just that , a lack of continuity that interrupts an electrical signal and can be a poor connection anywhere in the circuit .

My Freightliner has the VDC ( VDU ) electronic gauge package that preceded your MMDC , I haven't had a chance to be hands on with the MMDC , but here's some info I've acquired over the years.

RV Tech Library - Freightliner MMDC Information Display
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Old 02-05-2023, 07:36 AM   #9
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Quote:
Originally Posted by Skip426 View Post
Ronnie, has touched on a possible cause of your issue ; which is an intermittent open circuit , not a short.



Shorts , burn out fuses and wiring .



Open circuits , are just that , a lack of continuity that interrupts an electrical signal and can be a poor connection anywhere in the circuit .



My Freightliner has the VDC ( VDU ) electronic gauge package that preceded your MMDC , I haven't had a chance to be hands on with the MMDC , but here's some info I've acquired over the years.



RV Tech Library - Freightliner MMDC Information Display


Hey Skipó-called them yesterday after reading Ronnieís post which makes the most logical sense to me. Also was reading some off the pdf someone sent and page one was defining the idiot light chase problem Iíd have from time to time, if the coach loses signal from ECM for more than fifteen seconds, the light bar goes through that process. So that explains that. Anyway, FYDA spent another half day trying to figure it out and came up short again. So now I have at 12 to 15 hours labor tied up with this and nothing to show for it. So I when I get time Iím just gonna pick it up and get it home. Donít quite know how, but a serious debate with their service manager over this bill will have to be addressed. I donít see where this is any different than them hiring me to deliver a truck from their yard to a customer and me not being able to figure out how to get the thing out of the yard but still wanting to be paid for the job! But I will certainly check the connections on this module before I leave. Thank you people!
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Old 02-05-2023, 01:01 PM   #10
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Well Sir, does this bring back BAD memories!!!!!!!! You see, we had the almost same EXACT presenting symptoms in our coach. By the way, ours is an '04 Itasca Horizon 36GD with the CAT C-7 330HP and Allison MH3000 Trans. The chassis build date is 10/03 and the coach build date is 11/03 and first put into service 1/04.

What this all means is, ours is one of the first chassis's by Freightliner with not only the newer version 330HP engine known as the C-7, but also, it's also one of the first to be fitted with the MMDC control computer. The same assembly line at Freightliner, only a few rigs ahead of mine used the CAT 3126E 330HP and they also used the VDC platform for controlling and interpreting data to be fed to your gauges. Oh, by the way, VDC is Vehicle Data Computer and MMDC is Multi-Module-Data-Controller/computer.

Also, the earlier chassis's than yours and ours used the J1578 data network and ours uses the newer J1939 data network.

Basically, it (the data network) works like this: The MMDC is basically an interpreter for the many signals it receives and then sends to your dash instrument panel. Depending on which model coach one has, the MMDC can be located in various spots in or around the coach. In our Horizon, the MMDC is located on the back wall of the left front compartment. As stated, it receives data from your engine ECM, the transmission TCM, the ABS control module, and both primary and secondary/front and rear air systems. That MMDC with then interpret any and all signals from each of those components and send the results via a 21 pin plug to your dash for you to read.

Now, not only does that MMDC receive input from those stated components, it also receives and transmits INPUT DATA from you, the user. Such as, cruise control. If you ask for cruise control, all the parameters for cruise control to work must be in place. That is, feet off the brakes, and no exhaust brake or compression brake is in operation at the time of request. Once the parameters are in place, your request for cruise control is answered.

Now, back to your original issue. The "Bad memories" I stated are because we had the almost same exact scenario that you're experiencing. There's a decent difference in ours vs yours though. We were on a trip near Lordsburg NM on a very nice and smooth section of I-8 heading east about 11:30 in the morning. All was perfect. No traffic, road smooth, the CEO was dozing off and so was the mighty mini-Schnauzer. I was on cruise control at about 62 mph.

All of a sudden, the cruise control shut down, all on its own. I immediately looked at the gauges and NOTHING!!!!!!!!!!! That is, almost every single gauge was DEAD! The only one working was my fuel gauge. I immediately went into the panic mode. It's a good thing we were in almost zero traffic as the coach was slowing down rapidly. I thought, what the h....... is going on here??? For some odd reason other than maybe a natural reaction, I stepped on the gas pedal and, zooooooom, we were picking up speed!!!!!!!!!!!!!!!!

What?????????????? How in the world is this working? How can I pick up speed when my engine is DEAD and I have zero input to any and all gauges other than the fuel gauge? Well, the fact was, the engine WAS NOT DEAD it was running perfectly normally. The transmission was working perfectly normal. My brakes functioned as expected, perfect. Turn signals, lights, any input I put in, all functioned normally.

This all happened in about a 15-20 second time span. And then, I got a warning icon on my multi-colored icon panel. It said: "Check Info Center". That's the screen you see another poster showed in this thread. The info on that information center stated at that time, "No input from Engine/Trans in the last either 27 or 67 seconds" I can't remember if it was 27 seconds or 67 seconds, I know it was a 7. I had absolutely ZERO idea on what that meant.

The off ramp for Lordsburg was approaching rapidly. I took it. We pulled into a large empty parking lot next to a Carls Jr. The engine was idling just fine. I could take off from stop signs and stop lights perfectly. My brakes were fine. But, I had zero information on any gauge on the dash. CRAP!!!!!!!!!

Not a clue as to even THINK about where to begin to look for this issue.

So, I did what was the next best thing. I knew about the Freightliner hot line so, I gave them a call. After only a few minutes of conversation, the very knowledgeable person on the other end stated: "It appears you've lost communication with the J1939 Data line" I replied: What the heck does that all mean? Well, this nice lady didn't know my history of mechanical ability and just gave me a very brief explanation. I was still a tad confused but, she said my best move was, since the coach was still drivable, get it to a Freightliner service center.

She gave me three options. I picked one and we headed to El Paso TX to On the Border Freightliner. What a SERIOUS mistake. That's a whole 'nother story.

Anyway, to try and finish this up for you. After that incident, we decided to cancel our trip and head for home, no gauges and all. But, like you and your coach, every once in a while, we'd hit a bump on the freeway and, all of a sudden all my gauges would come alive. Then, right after that, they'd go dead again. CRAP!!!!!!! During the trip home, about 700 miles from El Paso to San Diego, those gauges would dance around on and off several times.

The MMDC and the J1939 uses only THREE WIRES to do all the communications between any and all components listed above. A yellow, a green and a black. The yellow and green are positive and negative of the system and the black is only a shield. Those three lines, are in basically a continuous loop. But, there are two terminating resistors installed in the system. One on each end. The resistors are there to stop signals from bouncing. The three wires, green, yellow and black, are not just in a straight line from one end of the coach to the other. They are TWISTED for the full length. They do that because that stops the attempt of outside electrical influence.

Now, here's the issue I had and, what was explained to me by Freightliner. The "No communication" info on that screen meant, something's gone wrong with one of the two wires, either the green or the yellow. One of them has somehow become disconnected or broken.

During the few days it was at the Freightliner dealer in El Paso, and while I had nothing to in that rat hole town, I learned a lot about that J-1939 system and the MMDC. As stated, that J1939 runs the full length of the coach. It is comprised of a main body and, what's called "branch" circuits. Each of the branch circuits are feed lines from the engine ECM or the trans TCM or the ABS module. The connections are all Deutch, well sealed connections.

The two resistors I spoke of are 60 ohm resistors. One is very close to the diagnostic port at the rear of the coach, located in one of the Deutch connections. The other is located in a very STUPID location. It's INSIDE the MMDC. If the one on the end near the diagnostic port goes out, it's no big deal to repace. If the one in the MMDC goes out, guess what, you need to spend over $475 for a new MMDC simply because a $3.00 resistor went south, smart move Freightliner!

Anyway, without a doubt, it was determined that we had a broken or bad connection with our J-1939 SOMEWHERE along 36' of coach! Freightliner in El Paso had zero idea on where to look and how to figure it out. They ordered and installed a brand new MMDC and that didn't do the fix! I told them to foget it and we're heading home. They tried like he... to make me pay for that MMDC. AIN'T GONNA HAPPEN!

Anyway, we got the coach home, no cruise and no exhaust brake so, I had to carefully plan the route due to no exhaust brake. But, I went to work trying to figure out how in the world to locate my problem. My coach looked like a bomb went off. I had every compartment open, the coach was 2' off the ground and wires were sticking out every where.

Now, here's the deal. When analzying the J-1939 for its very specific resistance, the 9-pin diagnostic port on the back is where this is done. And that resistance is not ADDED between the two 60 ohm resistors. Another words, when checking between pins C and D ( I think those are the ones, I'll have to re-check) in a normally working J-1939 data port, you are to get 60 ohms, plus or minus one or two max. If you see 120 ohms, HOUSTON, WE HAVE A PROBLEM!!!!!!!!!

And that was what I was getting when I was testing the two pins. CRAP! Now here's the saving grace in this whole story. My son, who's quite adept in mechanical skills (I have no idea where he got that from) came over for dinner and a hair cut. Mom does that for him. After dinner, he said, "let's go check it out". Now mind you, Freightliner in El Paso worked on this for three days.

My got on my creeper and stated, " so, your gauges would come back alive during SOME bumps on the freeway, correct? I said yep. We had the bed, over the engine completely removed so I could look at the engine and the ground at the same time. It was night time. He jumped on my creeper and scooted under the coach. He yelled at me to turn the key on and sit in the drivers seat and watch the gauges.

He found the J-1939 line and then started to twist and shake it, starting from the very rear and progressively moving forward. He had been working under there for approximately 5 minutes when, ZAP, my gauges started to work!!!!!!!!!!!!!! Then, they quit. Then, they worked, then they quit. The engine was running at this time so, we were communicating through some of those stupid little walke-talkies that came with the coach. Junk! Anyway, I jumped out of the drivers seat and ran to the back.

I told him "Stop, you're in the right area". I then went and shut down the engine. He said why do that, we can't find the issue now. I said, yes we can, all we need to do is, stick the pins of my VOM (Volt Ohm Meter) in the C and D ports of the J-1939 diagnostic port and watch the meter. He agreed. I rigged my pins up to stay in those two ports and turned on the meter and held it almost basically above where he was maneuvering those wires.

Amost instantly, my meter went from 120 ohms to 61 ohms. I told him, YOU'RE VERY CLOSE. He kept ever so slightly moving that J-1939 corregated tubing set of wires and that meter kept getting to 60 ohms until finally, it stayed on that setting. I told him, DON'T MOVE, I'm gonna start the engine. OK. I went and started it and, vuuuuuuuallllllaaaa, we had lift off!!! All the gauges were working flawlessly!!!!!!!!!!!!!!!! YAHOOOOOOOOOOOO!

He had narrowed the problem down to about a 1' section of that J-1939 line which, also included what's called a "Bulkhead" connector. That's a place where the J-1939 is connected together but is also held in place by a bracket extending from some part of the body or chassis.

He rolled out on my creeper and stood up and said, I FOUND IT, you FIX IT! AND HE LEFT. The next day, I rigged my VOM meter with some extra long leads and taped it upside down to the bottom of the frame near where he found the problem. I started doing the same thing he was doing, moving that J-1939 line around utill I narrowed it down to the connector.

I released it from that bulkhead fitting which was just above the differential and that allowed it to fall some so I could work on it. I unplugged the two ends. I couldn't see anything odd. He told me how to release the pins INSIDE that Deutch connector. So, I tried to release one of them and broke the connector, CRAP! So, since it was already broke, I just finished breaking it to release the other two pins in the male side. No issues there, all three wires were connected solidly to the pins that are inserted in that connector.

But, when I did the same to the famale part of that Deutch connetor, the black wire backed out fine, the yellow the same. But the green wire backed out WITHOUT A CRIMPED PIN ON IT. Hmmmmmm.

What was determined after all this was, when that green wire was being prepped by removing the insulation to install the pin, something went wrong with the tool that removes the insulation OR, the person operating the tool simply screwed up and not only removed the insulation but, about 98% of the copper strands of wires too. That coach's J-1939 had been operating on approximately TWO STRANDs of a 16 gauge green wire, for 49,000 miles. And finally, out of nowhere, on a very nice and smooth paved section of highway, those two remaining strands of wire finally gave up the ghost!

And the thing is, the reason I (and possibly you too) would see the gauges work every now and then was because those two strands of wire would be "bumped" together and make momentary contact and that would provide the communication of the J-1939 which, would allow the guages to work, MOMENTARILY!

Well, I didn't have the tools and or components to repair a Deutch connector. So, I called my son and asked if I could use a Weatherpack connector instead. He said yes. A connector is a connector. The wires don't care what type of connector is used, they only care about being connected. So, I broke out all my Weatherpack stuff and made a whole brand new setup. I connected the two ends together and, tested the ohms. 61, YAHHHOOOOOOO.

I went into the coach and started the big CAT up and, vuaalllla, Houston, our problem is fixed!

So, sorry for the really long story but, I wanted you to know just that, it's possible, POSSIBLE that you're in the same boat as we were. Is it a bad ground, maybe. Is it a J-1939 data link loss in communication, possibly.

At this point, my suggestion would be to test the ohms between pins C and D on the J-1939 diagnostic port. If it works, here's some info on that J-1939 diagnostic port and pin-out.
Scott
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File Type: pdf J1939 testing data.pdf (974.9 KB, 5 views)
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Old 02-05-2023, 02:20 PM   #11
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I had the same problem on my 04 chassis. My solution turned out to be the harness plugs on the MMDC control module. The module is located in the front drivers side compartment where all the fuses and electircal components are located. There are two connectors, a wide one and a narrow one. I had to remove the connectors, clean the pins and sockets with contact cleaner and small brush [tooth brush], coat with dieelectric grease and replug making sure not to damage the pins. I have not had an issue since.
Good luck
.
Ronnie


Yeah Ronnie!!! I am definitely going to check this out! It certainly makes the most sense and after viewing part of the pdf pertaining to the module, it would appear as it also would be the culprit causing the light bar chasing problem. Thank you very much!
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Old 02-09-2023, 03:15 PM   #12
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Yeah Ronnie!!! I am definitely going to check this out! It certainly makes the most sense and after viewing part of the pdf pertaining to the module, it would appear as it also would be the culprit causing the light bar chasing problem. Thank you very much!


Hey Ronnie and Skip. Had a load through Columbus today so I stopped in to settle up. Was all prepared for a heated argument over this labor and nothing to show for it, but the shop manager did me a decent. Still way too high but could have been a lot worse. So OK, I was all excited about the harnesses in this module, but it is no where to be found in my fuse and breaker box. Iím going to try and send a pic of what I have. Took the cover off the fuse panel for effect. I did notice the assembly date of the coach was January 2004. So I guess I got one of the crossover headaches huh? Did not pull the dash cover off to look in there,figured Iíd better get her home first. Did drive it around the lot for a few minutes and everything was working fine. Too damn windy up here today to take it out on the road. So hereís what Iím looking at and where do you think I go from here?Click image for larger version

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Old 02-09-2023, 03:47 PM   #13
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meyr,

Well Sir, does this bring back BAD memories!!!!!!!! You see, we had the almost same EXACT presenting symptoms in our coach. By the way, ours is an '04 Itasca Horizon 36GD with the CAT C-7 330HP and Allison MH3000 Trans. The chassis build date is 10/03 and the coach build date is 11/03 and first put into service 1/04.



What this all means is, ours is one of the first chassis's by Freightliner with not only the newer version 330HP engine known as the C-7, but also, it's also one of the first to be fitted with the MMDC control computer. The same assembly line at Freightliner, only a few rigs ahead of mine used the CAT 3126E 330HP and they also used the VDC platform for controlling and interpreting data to be fed to your gauges. Oh, by the way, VDC is Vehicle Data Computer and MMDC is Multi-Module-Data-Controller/computer.



Also, the earlier chassis's than yours and ours used the J1578 data network and ours uses the newer J1939 data network.



Basically, it (the data network) works like this: The MMDC is basically an interpreter for the many signals it receives and then sends to your dash instrument panel. Depending on which model coach one has, the MMDC can be located in various spots in or around the coach. In our Horizon, the MMDC is located on the back wall of the left front compartment. As stated, it receives data from your engine ECM, the transmission TCM, the ABS control module, and both primary and secondary/front and rear air systems. That MMDC with then interpret any and all signals from each of those components and send the results via a 21 pin plug to your dash for you to read.



Now, not only does that MMDC receive input from those stated components, it also receives and transmits INPUT DATA from you, the user. Such as, cruise control. If you ask for cruise control, all the parameters for cruise control to work must be in place. That is, feet off the brakes, and no exhaust brake or compression brake is in operation at the time of request. Once the parameters are in place, your request for cruise control is answered.



Now, back to your original issue. The "Bad memories" I stated are because we had the almost same exact scenario that you're experiencing. There's a decent difference in ours vs yours though. We were on a trip near Lordsburg NM on a very nice and smooth section of I-8 heading east about 11:30 in the morning. All was perfect. No traffic, road smooth, the CEO was dozing off and so was the mighty mini-Schnauzer. I was on cruise control at about 62 mph.



All of a sudden, the cruise control shut down, all on its own. I immediately looked at the gauges and NOTHING!!!!!!!!!!! That is, almost every single gauge was DEAD! The only one working was my fuel gauge. I immediately went into the panic mode. It's a good thing we were in almost zero traffic as the coach was slowing down rapidly. I thought, what the h....... is going on here??? For some odd reason other than maybe a natural reaction, I stepped on the gas pedal and, zooooooom, we were picking up speed!!!!!!!!!!!!!!!!



What?????????????? How in the world is this working? How can I pick up speed when my engine is DEAD and I have zero input to any and all gauges other than the fuel gauge? Well, the fact was, the engine WAS NOT DEAD it was running perfectly normally. The transmission was working perfectly normal. My brakes functioned as expected, perfect. Turn signals, lights, any input I put in, all functioned normally.



This all happened in about a 15-20 second time span. And then, I got a warning icon on my multi-colored icon panel. It said: "Check Info Center". That's the screen you see another poster showed in this thread. The info on that information center stated at that time, "No input from Engine/Trans in the last either 27 or 67 seconds" I can't remember if it was 27 seconds or 67 seconds, I know it was a 7. I had absolutely ZERO idea on what that meant.



The off ramp for Lordsburg was approaching rapidly. I took it. We pulled into a large empty parking lot next to a Carls Jr. The engine was idling just fine. I could take off from stop signs and stop lights perfectly. My brakes were fine. But, I had zero information on any gauge on the dash. CRAP!!!!!!!!!



Not a clue as to even THINK about where to begin to look for this issue.



So, I did what was the next best thing. I knew about the Freightliner hot line so, I gave them a call. After only a few minutes of conversation, the very knowledgeable person on the other end stated: "It appears you've lost communication with the J1939 Data line" I replied: What the heck does that all mean? Well, this nice lady didn't know my history of mechanical ability and just gave me a very brief explanation. I was still a tad confused but, she said my best move was, since the coach was still drivable, get it to a Freightliner service center.



She gave me three options. I picked one and we headed to El Paso TX to On the Border Freightliner. What a SERIOUS mistake. That's a whole 'nother story.



Anyway, to try and finish this up for you. After that incident, we decided to cancel our trip and head for home, no gauges and all. But, like you and your coach, every once in a while, we'd hit a bump on the freeway and, all of a sudden all my gauges would come alive. Then, right after that, they'd go dead again. CRAP!!!!!!! During the trip home, about 700 miles from El Paso to San Diego, those gauges would dance around on and off several times.



The MMDC and the J1939 uses only THREE WIRES to do all the communications between any and all components listed above. A yellow, a green and a black. The yellow and green are positive and negative of the system and the black is only a shield. Those three lines, are in basically a continuous loop. But, there are two terminating resistors installed in the system. One on each end. The resistors are there to stop signals from bouncing. The three wires, green, yellow and black, are not just in a straight line from one end of the coach to the other. They are TWISTED for the full length. They do that because that stops the attempt of outside electrical influence.



Now, here's the issue I had and, what was explained to me by Freightliner. The "No communication" info on that screen meant, something's gone wrong with one of the two wires, either the green or the yellow. One of them has somehow become disconnected or broken.



During the few days it was at the Freightliner dealer in El Paso, and while I had nothing to in that rat hole town, I learned a lot about that J-1939 system and the MMDC. As stated, that J1939 runs the full length of the coach. It is comprised of a main body and, what's called "branch" circuits. Each of the branch circuits are feed lines from the engine ECM or the trans TCM or the ABS module. The connections are all Deutch, well sealed connections.



The two resistors I spoke of are 60 ohm resistors. One is very close to the diagnostic port at the rear of the coach, located in one of the Deutch connections. The other is located in a very STUPID location. It's INSIDE the MMDC. If the one on the end near the diagnostic port goes out, it's no big deal to repace. If the one in the MMDC goes out, guess what, you need to spend over $475 for a new MMDC simply because a $3.00 resistor went south, smart move Freightliner!



Anyway, without a doubt, it was determined that we had a broken or bad connection with our J-1939 SOMEWHERE along 36' of coach! Freightliner in El Paso had zero idea on where to look and how to figure it out. They ordered and installed a brand new MMDC and that didn't do the fix! I told them to foget it and we're heading home. They tried like he... to make me pay for that MMDC. AIN'T GONNA HAPPEN!



Anyway, we got the coach home, no cruise and no exhaust brake so, I had to carefully plan the route due to no exhaust brake. But, I went to work trying to figure out how in the world to locate my problem. My coach looked like a bomb went off. I had every compartment open, the coach was 2' off the ground and wires were sticking out every where.



Now, here's the deal. When analzying the J-1939 for its very specific resistance, the 9-pin diagnostic port on the back is where this is done. And that resistance is not ADDED between the two 60 ohm resistors. Another words, when checking between pins C and D ( I think those are the ones, I'll have to re-check) in a normally working J-1939 data port, you are to get 60 ohms, plus or minus one or two max. If you see 120 ohms, HOUSTON, WE HAVE A PROBLEM!!!!!!!!!



And that was what I was getting when I was testing the two pins. CRAP! Now here's the saving grace in this whole story. My son, who's quite adept in mechanical skills (I have no idea where he got that from) came over for dinner and a hair cut. Mom does that for him. After dinner, he said, "let's go check it out". Now mind you, Freightliner in El Paso worked on this for three days.



My got on my creeper and stated, " so, your gauges would come back alive during SOME bumps on the freeway, correct? I said yep. We had the bed, over the engine completely removed so I could look at the engine and the ground at the same time. It was night time. He jumped on my creeper and scooted under the coach. He yelled at me to turn the key on and sit in the drivers seat and watch the gauges.



He found the J-1939 line and then started to twist and shake it, starting from the very rear and progressively moving forward. He had been working under there for approximately 5 minutes when, ZAP, my gauges started to work!!!!!!!!!!!!!! Then, they quit. Then, they worked, then they quit. The engine was running at this time so, we were communicating through some of those stupid little walke-talkies that came with the coach. Junk! Anyway, I jumped out of the drivers seat and ran to the back.



I told him "Stop, you're in the right area". I then went and shut down the engine. He said why do that, we can't find the issue now. I said, yes we can, all we need to do is, stick the pins of my VOM (Volt Ohm Meter) in the C and D ports of the J-1939 diagnostic port and watch the meter. He agreed. I rigged my pins up to stay in those two ports and turned on the meter and held it almost basically above where he was maneuvering those wires.



Amost instantly, my meter went from 120 ohms to 61 ohms. I told him, YOU'RE VERY CLOSE. He kept ever so slightly moving that J-1939 corregated tubing set of wires and that meter kept getting to 60 ohms until finally, it stayed on that setting. I told him, DON'T MOVE, I'm gonna start the engine. OK. I went and started it and, vuuuuuuuallllllaaaa, we had lift off!!! All the gauges were working flawlessly!!!!!!!!!!!!!!!! YAHOOOOOOOOOOOO!



He had narrowed the problem down to about a 1' section of that J-1939 line which, also included what's called a "Bulkhead" connector. That's a place where the J-1939 is connected together but is also held in place by a bracket extending from some part of the body or chassis.



He rolled out on my creeper and stood up and said, I FOUND IT, you FIX IT! AND HE LEFT. The next day, I rigged my VOM meter with some extra long leads and taped it upside down to the bottom of the frame near where he found the problem. I started doing the same thing he was doing, moving that J-1939 line around utill I narrowed it down to the connector.



I released it from that bulkhead fitting which was just above the differential and that allowed it to fall some so I could work on it. I unplugged the two ends. I couldn't see anything odd. He told me how to release the pins INSIDE that Deutch connector. So, I tried to release one of them and broke the connector, CRAP! So, since it was already broke, I just finished breaking it to release the other two pins in the male side. No issues there, all three wires were connected solidly to the pins that are inserted in that connector.



But, when I did the same to the famale part of that Deutch connetor, the black wire backed out fine, the yellow the same. But the green wire backed out WITHOUT A CRIMPED PIN ON IT. Hmmmmmm.



What was determined after all this was, when that green wire was being prepped by removing the insulation to install the pin, something went wrong with the tool that removes the insulation OR, the person operating the tool simply screwed up and not only removed the insulation but, about 98% of the copper strands of wires too. That coach's J-1939 had been operating on approximately TWO STRANDs of a 16 gauge green wire, for 49,000 miles. And finally, out of nowhere, on a very nice and smooth paved section of highway, those two remaining strands of wire finally gave up the ghost!



And the thing is, the reason I (and possibly you too) would see the gauges work every now and then was because those two strands of wire would be "bumped" together and make momentary contact and that would provide the communication of the J-1939 which, would allow the guages to work, MOMENTARILY!



Well, I didn't have the tools and or components to repair a Deutch connector. So, I called my son and asked if I could use a Weatherpack connector instead. He said yes. A connector is a connector. The wires don't care what type of connector is used, they only care about being connected. So, I broke out all my Weatherpack stuff and made a whole brand new setup. I connected the two ends together and, tested the ohms. 61, YAHHHOOOOOOO.



I went into the coach and started the big CAT up and, vuaalllla, Houston, our problem is fixed!



So, sorry for the really long story but, I wanted you to know just that, it's possible, POSSIBLE that you're in the same boat as we were. Is it a bad ground, maybe. Is it a J-1939 data link loss in communication, possibly.



At this point, my suggestion would be to test the ohms between pins C and D on the J-1939 diagnostic port. If it works, here's some info on that J-1939 diagnostic port and pin-out.

Scott


Scottó-I just now found your response and made for a very interesting read. When I get home Iíll check this out. Very depressing dealing with things I just canít figure out. So if I locate the 3twisted wire harness, Iíve probably got the same setup as you I guess. But Iím definitely not gonna lose this thread. Really wish I understood ohms and electrical better.
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Old 02-09-2023, 04:32 PM   #14
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Meyer,
Ohms, and any electrical lingo is all Greek to me. I only know what I'm told and have done some VERY basic study on, like 12V. Things like when you have TWO 60 ohm resistors in a loop. If there's two, and they're in a loop, then why don't you ADD them? Heck, I don't know. All I know is, even with the two in that J-1939 Data link, you're still only supposed to get 60 + or - 1 or 2 when those pins are tested. But, if one goes south, either one, then the resistance jumps to 120, whaaaaaat? I'm clueless in this kind of stuff. I just know what I'm supposed to see on the meter when things are testing correctly.

Well, I see your problem may have been ironed out. That's great. And it wasn't the same as ours. That's REALLY GREAT! Because, finding a broken wire in a loom, entangled with a whole bunch of other looms, for 36', is one of the worst nightmares one could have on these dumb coaches.
Scott

P.S. On edit:
Meyer, I just took a quick look at your original post. No Sir, you will not find the MMDC in the area I described. It is only there, in that left front compartment on the two top-of-the-line diesels for Winne and Itasca of that era. And those were the Winne VECTRA and the Itasca HORIZON. The next step down from those two are the Winne Journey and the Itasca Meridian. In both of those coaches, If I'm not mistaken, you will find the MMDC INSIDE THE CAB, under the dash. I have no idea why they did that instead of placing it in the same compartment as the other models. But, it's what they did so, it is what it is.

By the way, in case you're interested, here's what the MMDC looks like.
Scott
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