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Old 11-28-2020, 02:05 PM   #1
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Join Date: Nov 2020
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Lack of Air System Audible Alarm

Hello all.
New to the RV world. Just purchased a 2005 Winnebago Journey 36G with the CAT 7 engine.
The issues I am having are with Air System indication. My rear air gauge is completely dead. My front gauge, and the customer air service point gauge are both reading correctly. When I start up, and the air pressure is below threshold, I get the warning light and warning on the engine monitoring device, yet no audible sound. Once the pressure eclipses the threshold, the warning light goes away. There are no alarms or warning lights associated with the rear air gauge at zero, nor are there any issues with Service Brakes, Parking Brakes, Engine Exhaust Brake, or Air Bags. The only other anomaly I can find is a pump that seems to continuously run in the LH side of the generator compartment, and a blue 1/4 in line in the same compartment that is dry rotted and not connected anywhere.
First off, does anyone have knowledge of the location of the actual buzzer/beeper/horn that is the audible alarm? Secondly, could this be a MMDC issue, and how would I troubleshoot this?
I am an aircraft mechanic by trade, so the actual work is no issue with me. The problem is finding reliable, complete, and pertinent information to follow. What better place to find such information than getting it straight form those who have dealt with it? Plus, after reading many posts, I am very hesitant to call Freightliner, or take it to a service center.
Any help is appreciated!
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Old 11-28-2020, 05:07 PM   #2
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Posts: 3,456
Have you swapped the gauges/wiring to see which end your problem is on? I believe Freightliner was running all the gauges on a multiplex string that year with a single wire feeding all. Swapping should tell you where to start, front or rear. Each gauge picks the data string it needs off the wire so hookup order is immaterial.

Although I'm not familiar with your specific coach, the warning buzzer is usually right behind the dash. On a 2005 Bounder I had the buzzer had a small screw in it that could be used to adjust the tone and loudness. My buzzer was about the size of a 50 cent piece, and about 3/4" thick, and black, of course..

Hope that helps.
2013 Tiffin Allegro Bus 43QGP
2011 Chevy Silverado 1500 Toad
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Old 11-28-2020, 10:50 PM   #3
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Location: Powell River, B.C.
Posts: 21,672
Because you chassis is less than 20 years old info on testing should be available from Freightliner's free help line .

No reading from the gauge would point me towards the gauge its self but if you don't get a low air alarm ; someone may have disconnected it .
I have diagnostic info for the VDC and LBCU systems, in use before and after, but not the MMDC.
Have them send you an air system diagram too.

Have your serial number handy and call ;
Freightliner help line .

Ask about joining DTNA Connect so you can get wiring diagrams and schematics , and part number info linked to your serial number .
THEN keep detailed notes , as F/L is slowly discontinuing support for the older chassis . My DTNA Connect access was terminated in May.

If you do get any diagnostic info , I'd like to have a copy .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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Old 11-29-2020, 01:45 PM   #4
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OK. I have found the Blue Line and where it connects. I will replace it today. AS for the Air Gauge, FL gave me the pass code to get into the diagnostic page, and test the gauges. The rear air gauge does not "sweep" so it is confirmed dead. I will remove the dash bezel today and check the wiring, and see if the buzzer is indeed disconnected.
Thanks all! More to come!
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Old 11-29-2020, 08:01 PM   #5
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Got the instrument enclosure removed and swapped the connectors on the air gauges. Confirmed bad gauge. Also found that the audible alarm had a pin detached from the rear of the connector. Reinserted and buzzer now works! Now the task of finding the gauge. Will call Freightliner tomorrow and have already emailed Medallion. We'll see.
Next step is to get the dash AC vacuum blue line replaced. At least the pump goes off when defrost is selected.
Thanks all for the help. Have a wonderful Christmas season!
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Old 11-29-2020, 08:06 PM   #6
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Location: Powell River, B.C.
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Tanks for the updates , hope the gauge doesn't cost .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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