Air Pressure erratic changes

[Steelersfan1]

I have been experiencing a problem with the air pressure monitoring system on my 2008 Sportscoach Pathfinder. The coach is built on a Freightliner XC Chassis and I have been reading a bunch of stuff about the VDC/VDU and the MMDC, however, I can't seem to find this "module" anywhere on the coach. I have traced airlines to every place I can think of on this thing and cannot find the module. Not sure it even has one - the green/red hoses that are suppose to be attached to this module run directly from the brake pedal module (just under the floorboard) to the to the gauges in the dash - I disconnected to hoses to see if there was a problem with moisture, but nothing but dry air came out of them. I have recently changed the dehydrator filter cartridge thinking that was the problem, but the problem still exists. The gauges will just suddenly drop to zero and the alarm will sound - still have plenty of air pressure but the behavior is erratic - sometimes the front gauge will drop and alarm, sometimes the back gauge will drop and alarm, some times they both go together. I believe this is an electrical problem with the computer that monitors the system, but cannot find any clear guidance online to resolve the problem. Any help from anyone out there would be greatly appreciated. Thanks. Jeff
2008 Sportscoach Pathfinder 384TS - 2007 Chevy Tahoe.

[Skip426]

Freightliners free help line 1-800-385-4357 ,have your serial number handy, may be able to help with approx. location. While your on the phone inquire about joining "Access Freightliner " for online access to parts and wiring info on your chassis.
The air lines attached to the VDC on my coach are 1/4" the smallest lines on the whole coach. I think I have a picture, if I can find it , I'll re-size it and re-post.

[Skip426]

Here is a picture, showing VDC, on the left , Trans controller , center, and VIM-V.
Air lines are visible lower left corner. Because F/L supplies a bunch of extra hose and wire in the harnesses the coach maker can relocate these modules. Mine are in the engine bay , passenger side, with the extra hose & wiring , they could be moved 4 > 5 feet from there.
Edit: Just realized there is nothing for scale in the photo. VDC is 8" square 1 1/2 " thick.

[Steelersfan1]

So I just got off the phone with Freightliner and they explained to me that the problem is actually with the jumper wires that connect all the gages together from the LBCU (Light Bar Control Unit) which was introduced into the XC-S Chassis in 2007 (hence the reason I have one of the first available). Apparently Coachman didn't do a very good job securing these wires under the dash and over the years they have vibrated loose (at the plugs) causing the erratic behavior of the air pressure gauges and alarm. They have since developed a more robust harness/jumper wires which they are shipping to me this week. In the mean time, I will be disconnecting each section of the harness to clean each connection with an electronics cleaner and then reconnecting with some dielectric grease. This should work until the new harness arrives.

The representative at Freightliner told that this would definitely fix my problem - sure hope he was right - more to follow...

Jeff
2008 Sportscoach Pathfinder 384TS/2007 Chevy Tahoe/Blue OX

[Skip426]

Good that your not the only one to ever have this problem and that there is a fix. Hopefully the replacement parts are the cure.
Were you able to get info on MMDC location or do you even have one ?

[Skip426]

Jeff, It looks like your typing your coach info at the end of every post,
If you open the " User CP " on the blue bar left end, under the welcome message. Then go to " Edit Signature " on the left side of the User CP page and enter you info there. It will automatically appear below your posts , as mine does below.

[Steelersfan1]

Skip, thanks for the encouragement. Last night I disconnected each of the jumper wires starting from the LBCU - they are daisy chained from the LBCU to each of the gauges in the dash including the speedo and tachometer - sprayed each connector with electronics cleaner and then applied a small amount of dielectric grease and reconnected. I also secured the last jumper that left the temperature gauge and lead to the air pressure gauges - the jumper was about 24" too long and Coachman did not secure the wire at all under the dash. I coiled up the jumper and zip tied it to a secure location under the dash - Although I didn't have a chance to do an actual road test last night, I'm pretty confident that this temporary fix will hold me over until the new, more robust, harness arrives. I would also guess that this fix would most likely solve the problem permanently if the owner is willing to check the connectors periodically - it only took me about 45 minutes to pull the dash pieces off, clean and apply the grease. Although this may vary from coach to coach, it is a pretty simple and easy way to eliminate the problem. I do not believe that Freightliner continued to use the MMDC from 2007 on - the new LBCU is now the "brains" of all the indications. I traced the air lines from one end of the coach to the other and did not find any type of device that resembled the VDC/VDU or the MMDC. I did not ask the technician on the phone yesterday - I may call back today just to inquire about it. Thanks for you help and please feel free to share this with anyone else you might know who is experiencing similar problems. I will post the part numbers of the jumpers when I received them so they may be ordered by folks who are out of warranty (5 years).

[MiniFarmJeff]

I have a 2008 Coachmen Pathfinder 386qs. It too had this same problem. I was informed by Freightliner HELP center that my daisy chain wire harness was bad and if they are white,, they need the black wires.. I ordered the jumpers needed from Freightliner and installed them. If you have this same gauge cluster(see attached photos), I will list part numbers needed and which wire goes to what guage.
As you assemble the wire harnesses, looking at the gauges from sitting in the driver's seat, you will have two connections at each gauge on the back side of the guage. A left and a right as you sit in the seat looking at the gauges.

You will remove the old "white" harness one at a time...clean each of the "guage" connections with a plastic safe electrical contactor cleaner and add a dab of dielectric grease to each end of the jumper.

To start, I am going to list the part # starting at the Air #1 gauge that jumps to Air #2 guage. You will use part # POL028A274098004...this part goes from #1 to #2 gauge and has a "y".

From here, you will need 6 each of part # A06-69136-012 and connect each to the following...

From the "y", connect the A06-69136-012 to the "Y" and to the fuel gauge connect left side(looking at it from drivers seat)

Place the next wire from the right side of the Fuel guage to the left side of the Water temp gauge

Place the next wire from the right side of the Water Temp to the left side of the Tach

Place the next wire to the right side of Tach to the left side of the Speedometer

Place the next wire from the right side of the Speedometer to the left side of the Battery guage

Place the next wire from right side of the Battery guage to the left side of the oil gauge

Now you will need part # A06-69135-012
This part will need to attach with the Ball of the harness closest to the backside of the LBCU display screen and the longer end of the pigtail will attach to the Oil guage right side.

So to recap you will need from Freightliner:

1-A06-69135-012
6-A06-69136-012
1-POL028A274098004

Hope this helps someone with the same issue...I ended up purchasing more wires than needed...the 012 at the end of the of the part numbers means it is 12 inches long....there are a couple harnesses that will say 048 for 48 inch and a 063 for a 63 inch.

Jeff W