Air Brakes Warning System - Pressure Guage Erratic Reading

[dickandlois]

Txphantom,

Welcome to FMCA.

This sounds like a common problem for your year FCC Chassis.

There is a module / box located under the bed in many cases with Red and Green 1/4in. air lines connected to it. This box reads the air pressure and sends the information to your gauges.

There have been a number of problems with the large solder connections. Some have replaced the unit at a cost of around $1000.00.

Others have had the skills and tools to repair these solder connections. There is a procedure for repairing the board.

You can contact me by Private Message, click on my Name above the picture opens a new page and look for the send me a message feature and contact me if you want more information.

Rich.

[Blazeracing]

Hello fellow rv'ers

I am glad google lead me to this site. Seems very helpful. I too have a 2000 Fleetwood discovery on a Frieghtliner chassis. Both of the air gauges act strange dropping to 0 and back to normal.

But I thought it was something wrong behind the gauges because I can hear something kinda whirl and grind as the gauges fluctuate. I'm just wondering if I have different problem then the module back under the bed. I plan in looking into the module tomorrow. Seems like logical place to look.

[dickandlois]

Hi Blazeracing, Welcome to FMCA and good morning!!

The problem is 99.9% in the module, caused by a cold solder connection or two.

The sound you are hearing is likely coming from the Gauges. Bet it's a very soft sound, that the gauge makes as the readings come and go. I'm thinking you also have very good hearing !! ?

That being the case, there are a number of us that would be willing to rent out your services. Our DW's often mention; you don't hear the sound coming from wherever. LOL

Rich.

[fad847]

Many good suggestions, i'll try a few and keep you updated. Thanks

[klparker]

I have a 2001 Itasca Horizon. Over last six months I have to wait longer between starting out for the air to build up on gauges and brake alarm to go off. Now, I have no air pressure on either front or back gauges and brake alarm continues. I have let engine idle for 15 minutes to no avail. Any suggestions on what I should be looking at. Thanks!

[wolfe10]

klparker,

Welcome to the FMCA Forum.

First thing is to determine if this is a real problem (no air pressure) or gauge problem.

After the engine has been running long enough that is should have built air pressure (and did before the problem started), turn off the engine.

Walk around the coach and listen for an air leak-- if so, fix. If not, continue.

Push in the parking brake plunger (to release the parking brake). Does it release? If so, you have 40+ PSI.

Re-apply parking brake. Lightly pump service brake 5 times. Again try to release the parking brake. If it does, you very likely have a gauge, not air pressure problem.

If you have a build-in air chuck, you could also check pressure there.

If it truly is an air pressure issue, start by replacing the AIR GOVERNOR-- not expensive or difficult to replace. It turns the engine-driven compressor "on" and "off" (actually loads and unloads the compressor valves).

[klparker]

Thanks, will try and get back to you after snow melts enough to get to coach.

[markstella]

I had the same problem with my 2000 Horizon on a Freightliner. Turned out to be an instrument control modular. The original part had a letter " A " in the part number . The new one at that time had a letter " E ". Indicating to me that this part has been updated several times.

[huffypuff]

Thanks, will try and get back to you after snow melts enough to get to coach.

If you are in cold weather there is a possibility that the governor is frozen from the cold weather and may free up once the engine gets warm. It easy to remove that governor and clean it in a pinch but always better to replace. It's common for it to get corroded if water gets into it.

[klparker]

Could not locate/hear any air leaks. I cannot locate the governor or the air compressor. Located the dryer and put air in it but no help. In addition, where would I find the instrument control modular - might as well check all items. I have 2001 Itasca with 330 CAT.

[wolfe10]

The air compressor is mounted ON the engine, passenger's side. The air governor will be either on it or near it between it and the air dryer (follow the air lines).

Do you have air at the air chuck (for filling tires)?

Did you do the check involving the parking brake-- results?

[ojsmithj]

I need help locating the "VDU" or "MMDC" on my 2007 Excursion with a CAT engine. I am having the same problem with both air gages reading erratically intermittently resulting in the low air pressure alarm sounding. I have reviewed all of the posts on the subject and agree that it has to be an indication problem as the brakes and air bags operate normally. My problem is finding the "VDU" or "MMDC". I traced the red and green air lines from the large valve located under the coach behind the left front wheel up to the back of each air pressure gage and there was not a "box" in that run. There is a compartment on the curb side behind the rear wheel with a decal on the door that reads "ATTENTION VEHICLE ECH, VIM, VDC LOCATED IN COMPARTMENT". There are 2 boxes in the compartment, one with a large 2 on the cover and the other with no markings. Neither box has air lines attached to it. I have searched the engine compartment, under the bed and under the chassis from front to rear without locating the subject box. The VIN# is 4UZACJDC57CY89100.

[dickandlois]

ojsmithj,

Welcome to the FMCA Forum!

Reading your post it sounds like you have covered the common locations

The Module(s) are generally under the bed in the bedroom, Freightliner tends to prefer placing them in the rear of the coach, but they could be in one of the rear storage bays.

For the air gauge unit, look for a Red an Green colored air line going to it, they use copper to send the information the the instrument panel.

So a call to Fleetwood customer service and your Fin number of the coach in hand. 800- 322-8216 They should be able to pin down the location.

This link might prove helpful.

http://www.fleetwoodrv.com/contact/

Rich.

[ojsmithj]

I have requested the info from Fleetwood but have not had a reply yet. Is there a possibility that the air pressure gauges are direct reading sense the "red" and "green" air lines go directly to the back of the gauges?

[dickandlois]

Should you have the plastic Red and Green airline tubing going to the back of the instrument panel pressure gauges, that would mean you gauges are reading the air pressure directly form the systems.

Do you have 2 gauges, one with a red Pointer and one with a Green pointer? or just one gauge with both(2) a red and green pointer?

Do both pointers move together, ( both going up and down equally or at different times? like one gauge drops and the other one is steady?)

Rich.

[ojsmithj]

There are 2 separate indicators, both with black pointers. They fluctuate separately. Some times only one gage drops off to 0 and then some times both are erratic. But in all cases the fluctuations are not synchronized. On startup, they both fluctuate until system pressure builds up and then they stabilize. They remain stable for awhile, some times as long as an hour or more, and then begin to fluctuate. That may last for a minute or two or some times up to five minutes.

[dickandlois]

ojsmithj,

Question, was it cold, like below freezing when this issue came up?

Could be water freezing in the air compressor Governor. It controls the air pressure and they get testy at times.

Do you pull the air drains from time to time to clear any water build up in the primary and secondary air tanks, and have you had the air dryer serviced? How long since it was last serviced?

Rich.

[ojsmithj]

If the governor was freezing wouldn't both gages fluctuate together, i.e. read the same at the same time? I drain the air tanks about every 6 months but have not serviced the dryer.

[dickandlois]

If the governor was freezing wouldn't both gages fluctuate together, i.e. read the same at the same time? I drain the air tanks about every 6 months but have not serviced the dryer.

For the most part, the Green / Primary air supply, supplies air to the rear brakes and supplies air to the Red / Secondary air supply for the air ride, so the red gauge will change more often then the green one.

When you mention fluctuation, are you seeing a rapid swing in pressures or swings that would be more in line with the Air Compressor cycling to maintain the air in both tanks ?

Rich.

[ojsmithj]

The fluctuation, when it occurs, is rapid and sometimes only occurs on one gage.

Then at other times both gages fluctuate but not at the same rate.

I strongly believe I have an indicator problem and not an actual loss of air pressure. I also think the air pressure gages are direct reading and not electrical.

[wolfe10]

A call to your chassis maker will quickly tell you what you have (in terms of mechanical vs electrical gauges) and also point you in the right direction for diagnosing the issue.

[klcracing]

I am having this issue with my 2007 FW Expedition. I have followed the red and green I/4" air lines out of the back of the gauges, thru firewall to up under motorhome to a pump looking item with bigger red and green air lines with two electrical items on them.

Is this the control modules? I have looked under bed, under closet access, in rear drivers side compartments looking for red and green 1/4 " air lines and haven't seen any. Can someone please post a pic of tcm so if I see anything like it I could look closer? Any and all help is appreciated.

[elkhartjim]

I am having this issue with my 2007 FW Expedition. I have followed the red and green I/4" air lines out of the back of the gauges, thru firewall to up under motorhome to a pump looking item with bigger red and green air lines with two electrical items on them.

Is this the control modules? I have looked under bed, under closet access, in rear drivers side compartments looking for red and green 1/4 " air lines and haven't seen any. Can someone please post a pic of tcm so if I see anything like it I could look closer? Any and all help is appreciated.

I'm going to assume you have a Freightliner chassis. Your problem could aslo be in the LBCU - Light Bar Control Unit. They sent me a new wiring harness and I've not had a air guage fluctation since.

[klcracing]

LBCU- is that the information bar and how did you find out it was the LBCU?

[elkhartjim]

LBCU- is that the information bar and how did you find out it was the LBCU?

Yes, that is the Information bar. I called the Freightliner Help Desk with my VIN. Its a known problem for my 2008 model year and it possibly includes the 2007. They changed the connectors on the wiring harness.

1-800-385-4357 Help Desk number 24/7/365