map40 wrote:
Yesterday I was driving my new (to me) Alfa See Ya 2005 with a 350 C7 on a Freighliner chassis with an Allison 3000MH trans, nicely between 65-68 and suddenly speedo went to zero, cruise kicked out and check engine light came on. Alarm said trans ecu no data 25 sec failure. Everything was working fine except the the speedometer, the millage counter, cruise control and engine braking. The allison display was working and the tranny was shifting OK, so I waited until it was safe to stop, shut down the engine, checked everything, restarted, and everything was OK. Drove another 120 miles, not a problem. I am assuming a connection problem between the trans ECU and the engine ECU, but I have no idea where they are in a Diesel coach. Any hel will be greatly appreciated!
map40,
Wow, you just described an almost identical scenario that we had a few years ago. There's a huge difference between what you've experienced and what we went though. Your's came back to life. Ours didn't. Ultra long story short. We too were cruising a long, heading east on I-10 very close to Lordsburg NM. Cruise control was on, wife was dosing off, freeway was smooth as glass, almost ZERO traffic at 11:30 A.M.
All of a sudden, bddddddddd, the the cruise shut off, the gauge panel all went dead and I thought "what the h..."? Just for the heck of it, I stepped on the gas pedal and, varrrrooooom, it took off!! I looked down at my Annunciator panel, (all the colored icon boxes) and, one said "check info center". So, I looked over at my Medallion Information center and it said, (same as yours) "No trans communication for over 25 seconds". It then switched to "No engine ECM data communication for over 25 seconds".
What in the world does all this mean? I didn't have a clue. All I knew was that, all my gauges were down, cruise control was in/op, exhaust braking was also inop. I had no idea what was going on, other than my engine was still operating just fine and, so was the transmission. An off ramp for Lordsburg was coming up rapidly so, off we went.
I pulled into a parking lot next to a McDonalds. I parked it and we went to lunch. Got back from lunch with a bald spot on my head from scratching it so much, trying to figure where to start here. As stated, it's a really, really long story but, here's the ultra short details.
What I learned during all this scenario is/was, starting in about late '03 and continuing up through at least maybe the '07 year models or so, there is what's called the "J1939" data link in Freightliner Coaches. The J1939 is simply a three wire wire system, that carries data from:
1. Engine ECM
2. Trans TCM
3. ABS module
With all three of those, in constant communication with also what's called the MMDC. The MMDC is, Multi-Module-Data-Computer (also known as "controller"). Anything and everything that has to do with communications between the engine and the trans, with your gauges, is process through the J1939 and the MMDC. The MMDC captures all that data and, interprets it, then processes it for distribution to all your gauges, for you to see and read.
And all of this is done through THREE WIRES. A Green, a yellow and a black. And in reality, it's really only done with two of those wires. The yellow and green, the black is merely a shield to keep stray electrical RF signals from interfering with the communications. The three wires are twisted together, all the way from the back of the coach, to the front of the coach. That twisting is also there for a reason.
There is a 120 ohm resistor, on each end of the data link. Those resistors are there to stop reflection of any communication signals from going back and forth.
I can go on for a few pages on this but, in our case, the green wire and or, one of it's connection pins in one of the Bosch triple sealed connectors, had failed. When that happened, I lost all communications with the J1939 and the MMDC. It took quite a bit of searching to find the broken spot but, my son and I did it and we were all fixed. There's a whole lot more to the story but, that's the meat of the matter.
As for yours, well, you had the same exact symptoms as I did. But, and this is a really BIG BUT, yours came back to life, after a short stop and re-start. Ours was dead, completely, THREE STATES AWAY FROM OUR HOME IN CA!!!
As any mechanic, worth their weight will tell you, an intermittent problem is the toughest problem of all automotive problems to fix. How do you fix something THAT'S NOT BROKE? So, with yours, who knows just what part OF ANYTHING that has to do with the J1939, might have developed a short glitch, and then corrected itself? Good luck Partner. Been there done that.
Scott
