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corprimo · 03-21-2015, 04:17 PM

2004 Journey with Cat C7, our first DP that we've owned for about a year, parked it behind our house with a cover over it back in October with everything functioning normally. It's a ice spring day today, so my wife and I removed the cover and went to start it up to move it onto our paved driveway. All the dash warning lights came on and stayed on, no gauges, and Medallion info shows nothing. ScanGuage D is showing engine info via 1939. Engine started up just fine, and coach seemed drivable, so we warmed it up on the road before parking it back in the driveway. No exhaust brake as well. Freight liner suggested a 5 amp or 10 amp Ignition fuse up forward, and those are OK. Any suggestions?

gatorcq · 03-22-2015, 08:54 AM

The gauges and dash lites are controlled by the MMDC. Black box under dash. It is possible a plug is loose or a bad ground.
The MMDC takes the signal from the ECU (Digital) and converts to Analog for the lights and the gauges.

corprimo · 03-22-2015, 10:51 PM

Thanks for the MMDC tip. We flew down to Portland to spend a week with grandkids while they are on spring break, so Coach will be waiting when we get back. What's the size of the MMDC? And what does MMDC stand for? I'll check with Freightliner again tomorrow.

FIRE UP · 03-23-2015, 12:00 AM

Quote:

Originally Posted by corprimo

Thanks for the MMDC tip. We flew down to Portland to spend a week with grandkids while they are on spring break, so Coach will be waiting when we get back. What's the size of the MMDC? And what does MMDC stand for? I'll check with Freightliner again tomorrow.

corprimo,
"MMDC" stands for: Multi-Module-Data-Controller. That box is about, 6" x 6" x about, 1" thick, if I recall. I had mine out on the kitchen table trying to see if I could tell if there was anything wrong with it when I had my problems. Yeah sure I could. It's one big printed circuit board. What am I going to do with a flash light and volt meter? NOTHING!

That MMDC, is located in different spots, depending on the year and model of the rig. On ours, it's located in behind the circuit breakers, inside the left front compartment. Our coach is an '04 Itasca Horizon 36GD with the C-7 330HP CAT. But, on most others, it's in a different spot.

As has been stated, that MMDC receives AND transmits data, to and from, the three major operational components your drive train. The engine ECM, the transmission TCM, and the ABS module. Through the J-1939 data link, all those components transmit data, to the MMDC which, interprets all of it and, then provides the appropriate data to both the analog gauges and, the digital ones too.

There are two other data links that are involve with data transmission too. One is the J-1587 and, the other is the J339.

Now, the J-1587, as I understand the scheme of things, is primarily used for communications between the two main modules, the Engine ECM and, the Trans TCM. It's also connected to the diagnostic ports, fore and aft. But, the J339 is the communication link, that is used for the transmission of data from the MMDC to both the Annunciator panel (Colored light bar) and, the Medallion Information Center.

All of those data links, are a twisted set of "three wires". The twist is there to stop interference from outside electrical influences. In the J-1939 data link, there are two, what's called: Terminating resistors. One on each end of the data link. One is very near the rear diagnostic port and may or may not be accessible from the rear of the coach. The other is INSIDE THE MMDC.

Those two resistors are there to stop "reflection" of signals being transmitted from components to and from the MMDC. As stated, there are three wires, all twisted together, for the entire length of the coach. There's a green wire, a yellow wire and, a black one. The black wire is known as a SHEILD. I forget what it's job is but, it's not as important as the two other wires.

The green wire, is known as the NEGATIVE of the data link and, the yellow wire, is known as the positive. It's basically a "loop". And, that loop is connected to those two resistors. There are a series of Bosch ultra weather sealed connections that make up that data link. The main line, that runs the length of the coach, is called the "Backbone" of the system. The side connections, i.e. the Engine ECM, Trans TCM, ABS Module and, MMDC connections are called: Branch legs.

OK, enough explanation for now. Here's a preliminary test, to the J-1939 system, that will tell you in short order if that system has any issues. It's a very simple test. It involves a volt-ohm meter. Since your utilizing the front diagnostic port for your Scangauge connection, you will have to utilize the rear diagnostic port for this test. If your remove the gray cap, (incidentally, do not loose that cap, it's $20 from Freightliner) you'll find 9 pins in that plug. They are labeled alphabetically.

The only two you're interested in are the "C and D" pins. Now, the two, terminating resistors have a value of, 60 ohms each. But, because they are linked in parallel in this particular circuit, the total value of the two together is, 60 ohms, not 120.

So, in this test, you set your volt-ohm meter to ohms and, the book says to disconnect the battery although it really doesn't matter. Your engine and ignition should be OFF for this test so, there will be NO 12v VOLTAGE IN THE CIRCUIT YOU'LL BE TESTING.

What you'll be doing is, touching the two pins, C & D with your test leads. It won't matter which lead is touching which pin. What your looking for is, something very close to 60 ohms. It may display on your meter as 61, 62, 59 etc. Much of that variance is based on the meter itself and, how well the test connections are.

But, if you encounter, 120 ohms, HOUSTON, WE HAVE A PROBLEM! The troubleshooting charts say that, if you have a result of 120 ohms, then you can have ONE of the two, resistors has given up the ghost or, you have a break in the J-1939, as I did.

But, I suspect, when you do that test, you'll find you have 60 +or - ohms on your meter. At this point in time, it sounds either like a lost ground in the front (dash area) of your system or, it's possible that the J339 data link has a bad connection or, like I had with the J-1939, A BROKEN WIRE! The J339 also has Dark green and yellow wires in its twisted setup. But, even though it's a twisted set, just like the J-1939, it's only connected in the front section, between the MMDC and the Annunciator panel and the Medallion Info Center.

OK, enough info for now. If you run that ohms test, please let me know what the results are will you. As state, if you come out with 60 ohms, you know that, that part of the communications, which is the BIG part, is functioning fine. That should lead you to a problem in the front section. Good luck.
Scott

corprimo · 03-23-2015, 11:03 PM

Thanks for all the great info. We'll be back in AK in a week and I now have specific things to look for. I suspect the MMDC is in the same place as yours, Scott, since both coaches are 36 foot 2004 models. Hopefully I can track down the problem and won't have to bring it in to the Anchorage Freight Liner dealer who charges 150 an hour to work on MH's. Other possibility is wires pulled loose from the instrument panel. Could be the culprit is all the freezing and thawing we've had this winter - one of the mildest we've ever had with very little snow.

FIRE UP · 03-24-2015, 10:29 AM

Quote:

Originally Posted by corprimo

Thanks for all the great info. We'll be back in AK in a week and I now have specific things to look for. I suspect the MMDC is in the same place as yours, Scott, since both coaches are 36 foot 2004 models. Hopefully I can track down the problem and won't have to bring it in to the Anchorage Freight Liner dealer who charges 150 an hour to work on MH's. Other possibility is wires pulled loose from the instrument panel. Could be the culprit is all the freezing and thawing we've had this winter - one of the mildest we've ever had with very little snow.

corprimo,
I'd bet dollars to donuts that your MMDC is in a different location from ours. The primary reason I say this is because, the Journeys and Meridians of the same year, are outfitted and compartmentalized differently. First off, you don't have your generator on "slide out" tray do you? Mine slides out the front end of the coach to expose the entire gen. Second, I'd bet your last compartment, on the passengers side, just in front of the duals, is your propane tank, correct? Mine is hanging on the frame, inside the coach. That compartment on my coach is a TV and other storage.

I'd bet that your left front compartment, in front of the left front tire, has no electrical components what so ever. Now, I could be wrong but, I'm PRETTY sure your coach is laid out the way I described. This means that, in that left front compartment, where I have miles of electrical looms, about 20 resettable 12V circuit breakers and, when I un-screw the panel that all those sit on and hinge it outwards, behind that panel lies my MMDC, my security module for all the auto-locking doors and compartment doors, my Smart Wheel Master Control, and more.

Let me know what you find out will you? Thanks
Scott

corprimo · 03-24-2015, 04:20 PM

You are absolutely correct on the difference in layout, so MMDC will either be under the dash (yuck) or in the front compartment above the non-sliding generator. I'll let you know when I get home and have a little time. This time of year I'm working part time training Motor Coach drivers for Holland America / Princess.

Dan

gatorcq · 03-24-2015, 07:42 PM

The MMDC is installed by Freightliner and not the OEM. During Camp Freightliner, Mike was very good at explaining location of MMDC and earlier VDC.

corprimo · 03-30-2015, 04:37 PM

OK, back in AK - not near as green here as OR this time of year! Scott, I ran the ohm test at the back on the J1939 port and got 60, so that's good! MMDC is located just forward of the steering column mounted to the firewall, so at least I know where it is. Lots of wires and stuff down there - plug in's are on top of the module and red/green airlines are on the rear. Need to figure out how get access behind the gauges/dash to check wire connections I guess, plus removing the carpeted left foot rest would help with access as well. Also catching up on a woodworking project and removing snow tires on my car...

FIRE UP · 03-30-2015, 08:05 PM

Quote:

Originally Posted by corprimo

OK, back in AK - not near as green here as OR this time of year! Scott, I ran the ohm test at the back on the J1939 port and got 60, so that's good! MMDC is located just forward of the steering column mounted to the firewall, so at least I know where it is. Lots of wires and stuff down there - plug in's are on top of the module and red/green airlines are on the rear. Need to figure out how get access behind the gauges/dash to check wire connections I guess, plus removing the carpeted left foot rest would help with access as well. Also catching up on a woodworking project and removing snow tires on my car...

corprimo
Well, the fact that your tests revealed 60 ohms is a real good thing. Because if it didn't, you'd be in for the search of your life. I know, 'cause I was there. But, at least that part of the investigation is going good. So, now, to get to the back side of the dash and gauges. I had a bad ground one time and, Freightliner customer assistance helped me right along and, within about 20 minutes on the phone, she had me all straightened out.

But, I'll be anxiously awaiting the next phase of your investigation results.
Scott

corprimo · 04-03-2015, 11:55 PM

Before I started unplugging things from the MMDC under the dash, I decided to try something my son recommended. I disconnected the ground wire on both battery banks. Then reconnected them, tightened all connections, and that fixed it. Warning lights did their 3 second test, then gauges came on, engine started, high speed idle, exhaust brake are all back. Even with the Coach battery switch on the dash turned off and the big chassis battery switch in the engine compartment turned off, there's still some juice to the front of the coach, so disconnecting ground wires is the only way to completely reset everything.

During the winter I had the coach parked in a gravel area at the back of our 2 acre lot alongside of a storage shed that has electricity. Every few weeks, I'd plug in the coach for a day or two. Once a month, I'd run the generator for an hour under load. One of those times I tripped the circuit breaker in the house for the circuit that went out to the shed, and I think it happened when I fired up the generator while plugged in to shore power. That may be what scrambled the MMDC. Glad it's functioning again, and love those easy fixes!