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J-1939 Data Link Short on J-1939 - wire from 6 Pin Deutsch Diagnostic Plug Only


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History of Problem:

1. After MH sat for about 6 weeks the Engine would not start and "Engine Communication Error" displayed on Dash.

2. Replaced 30 Amp Fuse in Rear Fuse panel and Engine Started about 5 times in a row.

3. Next Morning 30 amp Fuse Blown Again.

4. Investigated and found Battery + and - Pins burnt off at ECM Board.  Also found that power to Engine Board is directly from Battery and not thru Ignition Solenoid.  I believe this was so Solar can trickle charge Chassis battery but it also means power always on to ECM and VIM

5.  Replaced ECM and transferred ECM wires (30 or so) to ECM Connector on Chassis wiring harness.  I accidentally switch 1 of the 4 Battery +- Pairs and Fuse Blew.  I switched wires to correct and fuse did not blow and MH Started.

6. Silverleaf on front 6 Pin Diagnostic plug does not display any Engine Parameter but the Front Dash Gauges work.  I checked the front 6 Pin and rear 9 pin Deutsch Plugs with Engine Data Link Monitor and Rear rear Diagnostic Plug works and Front does not.  Silverleaf works on Rear Diagnostic Plug also.

7. Coach is drive-able but have 1 ECM Warning on Dash (SPN 558 FMI 5) when Engine is at idle.  As soon as I increase RPM the Warning clears and SPN 558 FMI 5 is gone.

8.  2 drive-able issues.

  Jake Brake does not work on either High or Medium position.  I believe the ECM believes that the Jake Brake is on.  So therefore the coach jerks when I take off from a stop light with light accelerator pressure but if I am able to accelerate more firmly not jerk.  I also believe that the ECM does not see from the front of J-1939 DL when I turn Jake Brake switch on or off.

   Cruise Control turns on but unable to activate.  The ECM does see that the Cruise Control is on or off.

9. Aladdin does not work for Engine Parameters.

10. Therefore, I decided I have a J 1939 data link problem.  I performed a Multi-Meter J -1939 DL 60 Ohm Resistor and J -1939 wire check.  The Resistor Check was good.  There was J-1939 no ground or power shorts on Rear 9 Pin  Diagnostic Pin.  On the Front 6 Pin plug, I did not do a Resister check but the J-1939 wire check showed a short or ground on the J-1939 - wire.

So, therefore I am looking for any help on this.  According to J-1939 trouble shooting steps, the next thing to do is to check for shorts or ground on the different J-1939 backbone segments.  Also if anybody has had J-1939 problems, is their a service center that was able to resolve the J-1939 problem.

 

Thanks Dean

2006 HR Navigator 43 PDQ

DD60 Engine

 

  

 

 

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I don't think it will help. But I will put it out here. I have a Scangauge D  that did not work on the front plug. It did work on the rear plug just fine.    After calling Scangauge D  support. They told me I could return it. Or buy a 50 foot Ethernet cable and run it off the rear port. Being that one did work that is what I did. No problems works great.

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BusNut: LOL...I hear you.  I actually thought of running a 50 foot USB cable for the Silver Leaf input to the PC to solve one gauge display but I would still have he problem of my Jake brake and cruise not working.  I am talking to RVE Service Center in Cogbug that are knowledgeable and they have given me some things to check.

Thanks Again.

Dean

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I bet you know that there is a USB cable length limitation and you may not find a simple working 50' cable. Hopefully you'll find a better fix and won't need repeaters.

/ I know this is obvious but I have two of the same plugs up front for the ISM and for Allison that could be confused for each other...

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Dean, you've troubleshot this issue to about the 90% level. Assuming you have the a chassis wiring diagram to your coach, you should be able to finish this off. As I understand it you do not see a short to ground at the engine end of the bus, but do at the instrument panel end. As you've noted, the next steps require you to go through isolating each of the segments to find what/where the short is. That is what a service center is going to do. They will be first charging you for validating what you've already discovered, and then going through the module discovery process, and then disconnecting each module from each segment, in the isolation process, all the while charging you by the hour. The problem is likely a chafed cable, in the harness. The J-1939 wires are buried in the wiring harness and are a twisted pair. There may be more than 1 set of twisted pair wires in the harness, one set for each wiring buses.
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Ivank: Yes, I was kidding on 50 feet of USB cable.  On my coach there is another 6 pin Deutsch plug connector but it is for the labeled for the VORAD diagnostic.

Thanks for input;

Dean

HP8850:

Thanks for the input and advice.  Since I am retired I plan to finish the diagnostics as you have described.  I talked to REV RV Service center in Coburg yesterday and they recommended the same procedure as you did and emailed me the Backbone and Jake Brake wiring diagram.  If I can not resolve I would probably take it there since they have resolved J-1939 DL problems before.  They were hesitant for a time estimate but they were confident they could resolve and fix in 8 hr. at $150 hr for $1,200.   As a starting point, REV RV recommended to start at the Aladdin and J-1939 Bridge at the center of coach.

Dean

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