Originally Posted by crusherbum18
A friend of mine has a 2008 34sle Alpine motorhome, it's in use regularly and for some reason it all of a sudden won't start. When he turns the key nothing happens but a code (J139) appears. He said it has something to do with the link between the engine and the transmision, anyone know what to look for? It is not a low voltage problem. Thanks in advance for any help on this situation.
This is going to be interesting. I could write about three pages of info here about his potential situation. You wrote "(J139)". There is what's called a "J1939" that is a high speed data link that connects the engine ECM, the transmission ECM, the ABS module and, depending on model year etc. it also is connected to what's called the MMDC or, in earlier years, the VDC. The MMDC is: Multi-Module-Data-Computer and, the VDC is: Vehicle-Data-Computer. Both of those computers, receive and translate/convert info from all the input modules into data that the gauges can read.
The J1939 is comprised of three TWISTED wires. A green (-), a yellow (+), and a black (shield). Very close to each end of that data link is what's called a "Terminating Resistor". Those resistors are there to stop what's called "Reflection" of data and signals generated by the ECMs etc. And, at each actual end of the J1939 are the diagnostic ports you see in or around the back of the radiator in many models and, up under the dash (pain in the a$$ to find) in the front. The data link is "Twisted" for a reason too but, I forgot why.
Most of the time, a failure of the J1939 will not cause an engine "no-start" condition. Most of the time, the J1939 is for transmitting data only. When ours quit, it was in the middle of the New Mexico desert, on I-10E, very close to Lordsburg. All the gauges, the cruise control, the exhaust brake etc. quit all at one time but, the engine kept on purring along and, the trans kept on performing just as it should.
My "Medallion Info Center" displayed: "No Engine or Trans ECM communications for over 25 seconds". Hmmmmm, what the heck does all that mean
Now, I'm certainly no expert on Freightliner or any other chassis manufacturer wiring but, I did learn a bit about the J1939 when ours quit/broke. As stated, it will be interesting to me if and when your buddy finds out just what the problem was/is on his coach. Please keep us informed of any findings and cure(s).