Gents,
I've searched and read many issues regarding the old "VDC" units and the newer MMDC units. I'm thinking I may have developed an MMDC issue. Here's the scenario. We're presently on vacation and all has been going well. We were on the freeway, I-10E, just outside of Lordsburg NM when all of a sudden, the speedo started dropping. I had the cruise set to 60. The speedo started dropping, stumbled a bit, then fell to zero.
The rig was corresponding to that too. In other words, the cruise had been shut down. Along with that, the tach went to zero, the oil pressure, water temp, turbo boost, and voltage gauges, all died. I think the air pressure gauges for both front and rear are still operative but, I can't remember (we're camped in Silver City NM right now). Another problem, and a serious one, the exhaust brake QUIT!
And, on my annunciator panel, the "ABS" has lit up, and "Check info center" is also lit up. When I look at the Medallion Info Center, it's reading "No data from Trans ECM and NO DATA from Engine ECM for 25 seconds", and is flashing that over and over.
Now, with all this going on, here's the deal. The engine is still running like a top. The trans is still shifting and operating flawlessly. All the lights, turn signals, brake lights and most other normal electrical stuff is still working just fine. And, I also have what's known as the "Trip-Tek" computer on board too. And, to those of you that don't know what that is, or don't have it, it's a system by which additional information, engine stats, trip odometer(s), maintenance items and more, are displayed on the monitor of the back up camera.
Well, since I lost all important gauges, I hit the Trip-Tek and all the engine stats, oil pressure, engine temp, trans temp, etc. are still just fine and operating just fine. My fuel gauge is working just fine.
Well, I pulled off the road, into town, and got lunch. Then we pulled the rig onto a side street and I called Freightliner help. They started to direct me to the MMDC 10-pin plug. They say those pins can get damaged due to the weight of the harness(s) in that area that tugging away at the plug. My phone was acting up too so I was in an out of the conversation with the Freightliner tech so, I thanked him for his time and went out and pulled that 10 pin plug and looked at it.
It looked just fine to me. Now, I also talked with my son, who works as an RV tech in San Diego and he has replaced many MMDCs due to faulty soldering on and in the pc board inside them. That's the same issues the older VDC units were having. What's up with these boys that do these boards? Anyway, to those who've had issues with the later MMDC units, did you have the same or close to the same symptoms? Is there a way to tell if the MMDC is actually bad without taking a chance on $400 or $500 worth of experimenting?
As stated, my speedo quit and so did my odometer. Now, to me, that's kind borderline "illegal" isn't it? I mean, heck you could drive that thing for another 100K miles and then get it fixed and, sell it as a "lesser mileage" vehicle". But, that's beside the points here. I sure could use some help here.
Scott
I've searched and read many issues regarding the old "VDC" units and the newer MMDC units. I'm thinking I may have developed an MMDC issue. Here's the scenario. We're presently on vacation and all has been going well. We were on the freeway, I-10E, just outside of Lordsburg NM when all of a sudden, the speedo started dropping. I had the cruise set to 60. The speedo started dropping, stumbled a bit, then fell to zero.
The rig was corresponding to that too. In other words, the cruise had been shut down. Along with that, the tach went to zero, the oil pressure, water temp, turbo boost, and voltage gauges, all died. I think the air pressure gauges for both front and rear are still operative but, I can't remember (we're camped in Silver City NM right now). Another problem, and a serious one, the exhaust brake QUIT!
And, on my annunciator panel, the "ABS" has lit up, and "Check info center" is also lit up. When I look at the Medallion Info Center, it's reading "No data from Trans ECM and NO DATA from Engine ECM for 25 seconds", and is flashing that over and over.
Now, with all this going on, here's the deal. The engine is still running like a top. The trans is still shifting and operating flawlessly. All the lights, turn signals, brake lights and most other normal electrical stuff is still working just fine. And, I also have what's known as the "Trip-Tek" computer on board too. And, to those of you that don't know what that is, or don't have it, it's a system by which additional information, engine stats, trip odometer(s), maintenance items and more, are displayed on the monitor of the back up camera.
Well, since I lost all important gauges, I hit the Trip-Tek and all the engine stats, oil pressure, engine temp, trans temp, etc. are still just fine and operating just fine. My fuel gauge is working just fine.
Well, I pulled off the road, into town, and got lunch. Then we pulled the rig onto a side street and I called Freightliner help. They started to direct me to the MMDC 10-pin plug. They say those pins can get damaged due to the weight of the harness(s) in that area that tugging away at the plug. My phone was acting up too so I was in an out of the conversation with the Freightliner tech so, I thanked him for his time and went out and pulled that 10 pin plug and looked at it.
It looked just fine to me. Now, I also talked with my son, who works as an RV tech in San Diego and he has replaced many MMDCs due to faulty soldering on and in the pc board inside them. That's the same issues the older VDC units were having. What's up with these boys that do these boards? Anyway, to those who've had issues with the later MMDC units, did you have the same or close to the same symptoms? Is there a way to tell if the MMDC is actually bad without taking a chance on $400 or $500 worth of experimenting?
As stated, my speedo quit and so did my odometer. Now, to me, that's kind borderline "illegal" isn't it? I mean, heck you could drive that thing for another 100K miles and then get it fixed and, sell it as a "lesser mileage" vehicle". But, that's beside the points here. I sure could use some help here.
Scott
dougmac wrote:
It actually is not as complicated as it can seem at first. It is a set of wires that carry data.
When am trying to find data wires, I look for the twisted pair of wires. Can you see the wires going into the back of the 10 pin connector? Is there a twisted pair?
"J1939" "Can bus" and Data link" are all pretty much different terms for this network.
dougmac,
On the back of my MMDC, the controller for the annunciator panel and all the gauges is a 24 pin connector and a 10 pin connector. Among all the wires that are entering the back of the plug to the 24 pin connector are two that appear to be the J1939 wires. They are green and yellow and are twisted. I got that far. But, from there, they travel deep inside that loom and go to who knows where.
If I were at home, in my own environment, and didn't have WIND BLOWING THE PAINT OFF THE RIG as it's almost been doing for the past three to four days, I'd do more to take this project on. But, being on the road, the wife and the dog with me, in not so good camp spots, Wind blowing everything, not having anywhere near all my tools, I'm really out of my element here.
This will be the FIRST TIME I've EVER had to PAY for someone to fix MY RV!!!! Boy, does that suck! I've got an appointment with Freightliner tomorrow morning at 08:00 to get this thing in there and see what they can come up with.
Scott
dougmac,
Thanks very much for sending that pic and info. I've done so much research the last two days that it's all turning to mush in the brain. Not that it was very clear in the first place. I'd sure like to be shown how to check this stuff out and where all the plugs etc. are. Trying to figure out what's what and where things are at is quite a chore.
We're presently in Silver City NM and the closest Freightliner service center is El Paso TX. He was fairly confident that it was the MMDC during the first part of the phone conversation with him but, as soon as I told him my fuel gauge is still working, and something else, he started aiming at the J1939 Data Link and or it's connections. Now, even though I've got your drawing and others now down loaded, I'm still thinking I'm way over my head.
This "Data Link" and "CAN BUS" stuff is lingo that's just a bit hard off my beaten path.
Scott
Thanks very much for sending that pic and info. I've done so much research the last two days that it's all turning to mush in the brain. Not that it was very clear in the first place. I'd sure like to be shown how to check this stuff out and where all the plugs etc. are. Trying to figure out what's what and where things are at is quite a chore.
We're presently in Silver City NM and the closest Freightliner service center is El Paso TX. He was fairly confident that it was the MMDC during the first part of the phone conversation with him but, as soon as I told him my fuel gauge is still working, and something else, he started aiming at the J1939 Data Link and or it's connections. Now, even though I've got your drawing and others now down loaded, I'm still thinking I'm way over my head.
This "Data Link" and "CAN BUS" stuff is lingo that's just a bit hard off my beaten path.
Scott
The J1939 data link is the network that allows controllers from different manufacturers to all communicate with each other.
The communication travels over a twisted pair of wires that connect all of the controllers together. (the wires are usually green and yellow) At each end of these wires there is a 120 ohm resistor. Here is a drawing I drew of how the network would be typically wired.
Because there is a 120 ohm resistor at each end of the backbone, there should be 60 ohms of resistance between the yellow and green wires at any point on the circuit.
You said there is a 10 pin connector. If you wanted to check to see if the unit was connected to the J1939 data link, make sure all of the controllers are powered down then identify the pins in the connector for the data link and check the resistance value between the two pins. If it is around 60 ohms, you are connected to the data link.
The communication travels over a twisted pair of wires that connect all of the controllers together. (the wires are usually green and yellow) At each end of these wires there is a 120 ohm resistor. Here is a drawing I drew of how the network would be typically wired.
Because there is a 120 ohm resistor at each end of the backbone, there should be 60 ohms of resistance between the yellow and green wires at any point on the circuit.
You said there is a 10 pin connector. If you wanted to check to see if the unit was connected to the J1939 data link, make sure all of the controllers are powered down then identify the pins in the connector for the data link and check the resistance value between the two pins. If it is around 60 ohms, you are connected to the data link.
dougmac wrote:
I am not following the acronyms ... but it sounds like you are talking about your electronic dash/info center. It sounds like the dash has lost its data connection to the chassis J1939 data link. If you can locate the connection where the data cable connects, the resistance between the two wires coming from the chassis should be around 60 ohms.
dougmac,
In essence, you're correct. I've talked with Freightliner on this and that's one explanation of the problem but, the other is the MMDC is possibly bad. Incedentally, the "MMDC" is the Multiple Module Data Computer. The "Medallion" information center is the receiving end of the MMDC and displays what the MMDC tells it to. My "Trip-Tek" is an option from Itasca/Winne that is an auxiliary way of observing engine ops, i.e. oil pressure, odometer(s), turbo boost, and many other instruments. And it shows all of it on the monitor of the Sony rear view/back up camera. So, in our rig, and I suppose many others out there, we have a redundancy of displays of engine info.
1, the gauges themselves
2, the Medallion Info Center
3, the Trip-Tek info system on the rear view camera monitor
all displaying much of the same thing. And yes, after talking with the service writer at a Freightliner Service Center in El Paso TX, he agrees that it's most likely a bad connection of the data link (J1939)to the MMDC. But, the MMDC is a runner up in this problem. So, we'll see. At this present time, I've got the MMDC off and in my hand. But, I have no idea what the "data link-J1939) looks like and how to check it. I was sent a trouble shooting schematic and guide but, so much of it is way over my head. Talk about Acronyms, wow, that document is full of them. Whew!
Scott
John Wayne,
Boy, you're close on this one I think. You see, I had an issue with the Annunciator panel and gauges a while ago. Long story short, A call to Freightliner and a nice lady talked me through some checks on that "10" pin connector on the back of the MMDC and, through her guidance, I found I had lost the grounds to that system. Now, not knowing where the grounds come from, I figure a ground is a ground, so, I made my own, "Tee-d" into the ground wires on the back of that 10 pin connector and YAHOOOOOOOOOO, it all started working again. Buzzers, gauges, annunciator panel, and all, went back to normal operation.
So, could this just be a bad ground, quite possibly but, where to check is the question. And, according to the trouble shooting schematic and guide that Freightliner sent me, You got to be real careful on your checking of certain wires or you could "Poof" some gauges!
Scott
Executive,
Yes Sir, that's one of the first things I checked prior to making the decision to drive this rig farther after I had this issue develop. I got out my little trusty volt/ohm meter and checked ALL the battery voltage. That's the chassis and house batteries while the engine was running. All were over 13 volts. Around 13.2 on the chassis and around 13.3 or so on the house batteries. So, that gave me the "go-a-head" to drive this thing to a nicer town. So, I'm pretty sure it's not the alternator. Thanks for the suggestion.
Scott
And thanks for all the help here.
