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10-23-2021, 10:02 PM
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#1
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Junior Member
Tiffin Owners Club Freightliner Owners Club
Join Date: Aug 2017
Location: Sun Lakes, AZ
Posts: 12
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Air Pressure Problem
The Low Air Pressure warning light came on and off a couple times on my 2009 Tiffin Phaeton 36QHS. Then the alarm came on and off along with the light. The secondary air pressure gauge started fluctuating between 45-120. Then the light and alarm came on and stayed on. The brakes worked normally the whole time. I turned the engine off and when I started it back up everything was back to normal. This has happened twice and each time it occurred after driving for about an hour. Anyone had a similar problem and knows how to fix?
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10-24-2021, 04:53 AM
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#2
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Senior Member
Winnebago Owners Club Ford Super Duty Owner
Join Date: Jul 2012
Location: Where the Rig is Parked
Posts: 1,398
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I believe that is an issue with the VDU unit or something similar to that name. It has been discussed many times that when that unit goes bad it creates that symptom.
Do a search here for VDU . . . Tons of info comes up on it
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10-24-2021, 06:15 AM
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#3
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Community Administrator
Tiffin Owners Club
Join Date: Sep 2013
Location: DFW, Texas
Posts: 21,557
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The other source for that type of problem can be a loose ground connection for the dash gauges. That can cause the intermittent drop out as you described.
__________________
2017 Phaeton 40IH XSH Maroon Coral - Power Glide Chassis with IFS
Previous '15 Tiffin Allegro RED 38QRA and '06 Itasca Sunrise 35A
'16 Jeep JKU Wrangler Sahara or '08 Honda Goldwing
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10-24-2021, 11:37 AM
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#4
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Senior Member
Fleetwood Owners Club Freightliner Owners Club
Join Date: Feb 2012
Location: Central Arkansas
Posts: 1,378
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There is page after page regarding similar issues with the Light Bar Control Unit (LBCU) and the twisted pair wiring that connects it and the gauges.
FL says the initial fix is to replace the white wires with the newer black ones. That works sometimes. Others were able to use a good contact cleaner (safe for plastic) and clean the connections.
Search for gauges and LBCU and prepare for lots of reading. I personally fought this and other gauge issues for years, and have now gone to a Fire Tablet velcroed to the dash with a BlueFire dongle plugged into the diag port under the dash. You still need the air pressure gauges though hooked to the LBCU as the data port doesn't send that data out from the ECM.
Best of luck.
__________________
2008 Fleetwood Bounder 38S 2022 Grand Cherokee WK Limited 2021 Polaris Slingshot R Limited
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10-24-2021, 11:38 AM
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#5
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Senior Member
Fleetwood Owners Club Freightliner Owners Club
Join Date: Feb 2012
Location: Central Arkansas
Posts: 1,378
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Quote:
Originally Posted by Ranger Smith
I believe that is an issue with the VDU unit or something similar to that name. It has been discussed many times that when that unit goes bad it creates that symptom.
Do a search here for VDU . . . Tons of info comes up on it
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I don't have info on when the VDU was no longer used...but I know that my 2008 and FredT's 2009 Freightliner chassis uses the LBCU and not a VDU.
__________________
2008 Fleetwood Bounder 38S 2022 Grand Cherokee WK Limited 2021 Polaris Slingshot R Limited
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10-24-2021, 09:07 PM
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#6
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Senior Member
Join Date: Apr 2011
Location: Powell River, B.C.
Posts: 31,486
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Quote:
Originally Posted by RichKimball
I don't have info on when the VDU was no longer used...but I know that my 2008 and FredT's 2009 Freightliner chassis uses the LBCU and not a VDU.
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VDC/VDU ( Vehicle Data Computer or Unit )was the first Freightliner electronic dash gauge control from 1999 to 2003 .
Then updated to the MMDC ( Multi Module Data Center ) to 2007.
Then the LBCU ( Light Bad Control Unit ) for which other members report installing a change up wiring harness.
__________________
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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11-17-2021, 07:04 AM
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#7
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Junior Member
Tiffin Owners Club Freightliner Owners Club
Join Date: Aug 2017
Location: Sun Lakes, AZ
Posts: 12
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Air Pressure Problem Fix
The Freightliner Service Center found “unit was equipped with old style daisy chain jumper harnesses, (white in color). Checked for proper terminal tension at jumper harness, found unit needs updated jumper harness, found weak connections at several jumpers. Found air gauges have integrated PSI Transducer for low air sensor warning, recommend replacing both air gages due to known internal circuit issues, air leaks.” Parts were $931.31 and labor to install was $928.20. Thanks to everyone who responded.
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