07 Fleetwood 38L Exhaust brake part II

[Shallow]

It seems my original post regarding the exhaust brake on my 07 Fleetwood 38L was too old to add a post to the thread. So, I've included a link to the original thread below and will briefly sum up the status.

http://www.irv2.com/forums/f26/07-fl...ak-191716.html

The exhaust brake stop functioning and I brought the RV to the local CAT service center. After more than 10 hours of trouble shooting without identifying the problem, they have a new solution.

They want to hard wire the exhaust brake switch directly to the CAT exhaust brake system and bypass the J1939 module. They believe the J1939 is the culprit and that this is the simplest and least expensive solution.

My only worry is possible unforeseen effects of bypassing the J1939, but feel I have little option remaining. I need the exhaust brake functioning and don't want to write a blank check to the service center to keep trouble shooting until I am bankrupt. Here we go. I'll keep all posted.

[Skip426]

Is the shop a combination Cat/ Freightliner , service center.
Do they have access to the wiring schematics for your chassis.
Not sure what the J1939 module is , and I'm guessing my coach doesn't have one, haven't seen it mentioned in my schematics.
While trying to help , Kuzzy, with his exhaust brake , I did discover some odd things about mine , multiple control relays. One in the VIM module and one just below it. You can just see the 4 wires running into it , below center of the second photo.
Without access to your schematics and coach , I don't know If you would have anything similar. But I hope, in 10 hours the service center has looked into all the possibilities.

[Skip426]

I shouldn't post when , I'm tired, like I was last night.
Questions I should have asked.

Does your shift pad , indicate down shift to second gear, when the exhaust brake should be operating ?
Have you contacted Freightliner yourself ?
Has the shop replaced any parts, in an attempt to fix your issue?

Freightliner free help line.
1-800-385-4357 have your serial number handy.
Inquire about joining , Access Freightliner , takes a while but well worth the wait.
Gives you access to wiring and parts info on line for your chassis.

EDIT: Second thought , I always have them. I've heard the J1939 reference to the diagnostic connector, on diesel MH's but not a specific module; so I've got some digging to do.

[FIRE UP]

Originally Posted by Shallow

It seems my original post regarding the exhaust brake on my 07 Fleetwood 38L was too old to add a post to the thread. So, I've included a link to the original thread below and will briefly sum up the status.

http://www.irv2.com/forums/f26/07-fl...ak-191716.html

The exhaust brake stop functioning and I brought the RV to the local CAT service center. After more than 10 hours of trouble shooting without identifying the problem, they have a new solution.

They want to hard wire the exhaust brake switch directly to the CAT exhaust brake system and bypass the J1939 module. They believe the J1939 is the culprit and that this is the simplest and least expensive solution.

My only worry is possible unforeseen effects of bypassing the J1939, but feel I have little option remaining. I need the exhaust brake functioning and don't want to write a blank check to the service center to keep trouble shooting until I am bankrupt. Here we go. I'll keep all posted.

Shallow,
I'm certainly no expert on any of this but, I have done some intense investigation of the "J1939" system because, ours went defective while on a trip. I don't know if you read my thread on it or not but, I explained all of what a J1939 is and does. Quite simply, a J1939 system is a standard put out by SAE and, is the operating system for communications between multiple modules in your coach. In all reality, it's only three wires. It's a green wire, (labeled as: Negative), a YELLOW wire, (labeled as: POSITIVE), and finally, a black shielded wire, used for shielding the other two to protect them from outside electrical interference. And, the entire J1939 system (all three wires) are "TWISTED" for the full length of the coach, also to protect against outside electrical interference.

The J1939 as stated, is the communication link or, "data link" as some prefer, between the Engine ECU, the Transmission C.U. the ABS MODULE, and finally on '04 and later coaches, what's called the MMDC. The MMDC is: Multi-Module-Data-Computer. It's main function is to accept messages sent from all the modules, (ones listed in previous sentence) and, interpret what's needed or, asked for. And, another function of the MMDC is to accept all sending unit signals, i.e. oil pressure, alternator output, water temp, air pressure and others, decipher them and, send those signals to the dash where you can read them and tell what's going on in and on your engine.

Now, like stated, the J1939 is only three, twisted wires, ran down the length of the coach, with "branch circuits" that lead to the engines ECM and all the others mentioned. There are separate and explicit tests for the J1939 to check it's functionality and to determine if there's issues with it. There's one more thing about the J1939 circuit. It's got two, 120 ohm resistors built into it. One is at one end of the system and, the other is at the other end. Those resistors help to stop what's called "reflection of signals" that are being sent by all the modules, to the MMDC.

One of the tests performed on the J1939 system is to see if the two resistors are still functioning. I won't go into the testing of them and, the results of those test(s) unless you ask. But, needless to say, they (the two resistors) must be present and, must be intact, for the J1939 to function correctly.

I was at a Freightliner shop for 2.5 days with a problem with mine and, the tech there was clueless on how to check the system out. That's when I dug into the "J1939" system and learned all about it. We brought the coach home, all the way from EL Paso TX, to San Diego without a functioning J1939 and, fixed it myself.

My point here is, there are items that must be in place, for your e-brake to work. One is, the throttle must be ALL THE WAY OFF, the next is optional, the cruise control for some coaches must be off, (our system in our coach does not require that) and, the engine ECM will "Ask" for the use of the e-brake, based on the parameters stated, before it will allow the e-brake to put into service. The J1939 communication system, is the system that controls all of this but, again, it's not a "module", it's only three wires. And, they either work, or the don't work. But, the testing of the "intactness" of the green wire and, the yellow wire, MUST BE PERFORMED, and, the testing of the ohms resistance of the two 120 OHM resistors MUST BE CHECKED, before ANYONE rules the J1939, is at fault, FOR ANYTHING!

Now, I don't know just how experienced your techs are that have been working on your coach so, I don't know if the correct tests on the J1939, have been done to determine its status. But, based on the research I've done, the articles I've read, the testing procedure that I've not only read about but, performed myself to see if my J1939 was/is in tact and working, if you had a "broken" J1939, you'd have much more problems than just a faulty e-brake. Because, as I understand it, and, EXPERIENCED IT, if it fails, so do most of the communications between the modules and the gauges on your dash.

So, I hope some of this explanation helps you, in helping them, to get your coach working correctly. Good luck.
Scott

Originally Posted by Skip426

Is the shop a combination Cat/ Freightliner , service center.
Do they have access to the wiring schematics for your chassis.
Not sure what the J1939 module is , and I'm guessing my coach doesn't have one, haven't seen it mentioned in my schematics.
While trying to help , Kuzzy, with his exhaust brake , I did discover some odd things about mine , multiple control relays. One in the VIM module and one just below it. You can just see the 4 wires running into it , below center of the second photo.
Without access to your schematics and coach , I don't know If you would have anything similar. But I hope, in 10 hours the service center has looked into all the possibilities.

Skip426,
Well Sir, the J1939 is really not a MODULE, in and of itself. As explained above, it's merely three, twisted wires, that link the many "modules" (engine ECM, transmission control module, abs control module and, the "Module" that receives all that info and spits it out on the dash, for you to read it. And, you're correct in assuming you don't have one. The J1939 was not designed when your coach was built. The "J1597" may have been but, not the J1939.
Scott

[Skip426]

You are correct, J1597, is the set up on my chassis.
Years of dealing with OBD at work , and I still haven't cross referenced what I remember from that to , diesel MH chassis diagnostics.

[FIRE UP]

Originally Posted by Skip426

You are correct, J1597, is the set up on my chassis.
Years of dealing with OBD at work , and I still haven't cross referenced what I remember from that to , diesel MH chassis diagnostics.

Skip,
I goofed up when I typed in the numbers for the system that's in your coach. It's the J1587, no 97. It's a slower operating system and works a bit differently than the J1939. Sorry about that. I wanted to correct that but, in this forum, once you've typed something in and, it's gone past an hour since you posted it, the "edit" function is removed. So, in the future, just for your information, you must edit things pretty close to when you posted it. No biggie.
Scott

[Skip426]

Originally Posted by FIRE UP

the "edit" function is removed. Scott

Been there , done that,

To show you you're not alone , before I posted , looked at my wiring diagrams , saw J1587, and still typed in J1597.
I've got to start writing this stuff down , now where did I put my pen ... paper..

[Shallow]

Skip426,

The shift pad does not immediately indicate ad downshift to gears 1-4 like it previously did when the exhaust brake functioned correctly.

And, the shop has replaced zero parts, purely checked functionality of the exhaust brake itself and ensured the wiring to/from the brake wasn't broken. They have also ensured that the switch on the console had not failed. They say they have access to the wiring schematics, but have not been able to identify the cause for the exhaust brake not working when desired.

The shop is a CAT repair shop and I have no idea if they are also a Freightliner repair shop, too. I suppose I should ask.

Thanks again for the Frieghtliner customer service number, I'll give them a shout.

[Shallow]

FIRE UP,

Thanks for the very detailed information regarding the J1939 link and its function on our RV's. It has got me thinking about some other abnormalities that I have noticed on my coach. First, the cruise control does not always function. It does most of the time, but I cannot duplicate the conditions that would identify any pattern to when it does or does not function. Also, the mileage when read from the maintenance pages of the dash display (I believe this to be reading it directly from the CAT engine) is accurate, but the normal mileage display on the Frieghtliner dash display is inaccurate, as well.

I wonder if these are related to the exhaust brake malfunction and are connected via the J1939?

[Skip426]

If the system ( trans and engine controllers) are seeing the , exhaust brake switch in the on position, but not activating the brake/ downshift cycle, when the coach is coasting; there could be an issue with the TPS,( Throttle Position Sensor) system wants to see zero TPS reading before starting the exhaust brake cycle.
I had a problem with a rusted pedal hinge; from carpet shampooing; causing jerking on acceleration, could be something similar on your coach.
Some members reporting problems ( mostly Cummins , equipped with adjustable pedals ) saying they have to lift the pedal with their toe to activate the brake.
On the erratic cruise operation. Mine wouldn't work if the roads were wet; traced back to corrosion between the terminals on the brake light switches, as soon as the corrosion got wet, enough micro voltage passed across the switch to have the engine ECM shut off the cruise control, because it thought the brakes were being applied.
I cleaned my switches and coated in silicone grease , no repeat issues in 3 years. Another member , reported that 2 new switches cured his problem.

[mchero]

Very good information here. Keep it comming!