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gene, RV Mechanic
Category: RV
Satisfied Customers: 1100
Experience:  28 yrs exp in the industry
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I have a 2008 Monaco Dynasty and am having J1939 problems. I

Customer Question

I have a 2008 Monaco Dynasty and am having J1939 problems. I can elaborate if this si something that is within your expertise.
Submitted: 1 year ago.
Category: RV
Expert:  Joe replied 1 year ago.

Hello, my name is Joe

I will assume your coach has a Cummins engine.

I you could respond with all of the fault codes stored in the engines ECM , that could be a big help in troubleshooting direction.

There are a variety of components on the data link that could cause a disruption in communication. Often the fault codes can give some direction in where to focus.


Customer: replied 1 year ago.
The tech started by checking the wiring that runs from what is called the light bar in the dash to to the left armrest. Apparently Monaco said that can be a problem area. I was getting an engine comm failure on the light bar. All appeared good but it appeared that at some point this was repaired ( must have been at the factory). He built a new harness to the armrest. problem returned . It only happens when the ambient temp is over 70 and the engine is working hard. gauges go nuts lots of idiot lights. Loss of power, no jake brake. When engine load returns to normal problem goes away. Tech has suggested that the problem may be in that light bar. he says it is a controller. I have since found that there is a J1939 "bridge" box in the ceiling of one of the bays. But all appears to look ok. No loose connections or bad wires. I also did a google on this subject other Monacos have had this problem. I don't know the fault codes but the work order says they are all comm faults. Others have found : a bad fuse, a loose connection or corroded connection. Tech thinks he could open up the light bar and if it is a bad board he could re[pair it. I haven't tried to buy a new one. To build a new harness would cost a fortune. I suggested that maybe the ECM is bad. tech says no. Tech has a lot experience with J1939 problems in FL trucks as well as a few Monacos. I am trying Just answer in the hope of finding a tech who has fixed this problem. My tech is a Cummins/electronic/electrical specialist as well as shop foreman at a FL dealership..
Expert:  Joe replied 1 year ago.

Thanks for the update,

Since it happens most frequently with high engine temps.

Without the fault codes and number of fault counts available, I would suggest focusing on j1939 components and connections in the engine bay.

I will opt out of the question to allow other experts to respond.