My speedometer has started acting up. It will register approximately the correct speed after sitting for some time, but then slowly the indicated speed decreases with time until it eventually gets close to zero after a few hours. The odometer seems to be working fine, and the cruise control as well. Tachometer also working fine. Everything else seems to work well including transmission. I have read that it may be a bad ground wire, but wouldn’t that also affect the odometer? Thanks for any help.
2006 Sportsman Cross Country 370 DS with Cummins 5.9 and Allison 300 tranny
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My speedometer has started acting up. It will register approximately the correct speed after sitting for some time, but then slowly the indicated speed decreases with time until it eventually gets close to zero after a few hours. The odometer seems to be working fine, and the cruise control as well. Tachometer also working fine. Everything else seems to work well including transmission. I have read that it may be a bad ground wire, but wouldn’t that also affect the odometer? Thanks for any help.
2006 Sportsman Cross Country 370 DS with Cummins 5.9 and Allison 300 tranny
I'd grab a can of CRC contact cleaner and lubricant, pull the dash and then remove each connector from the LBCU (or you may have the other "brain" - but both have daisy chain wiring to all the gauges, which is the problem) than I'd spray each plug and socket and stick it back in a few times.
While back there, you'll find a buss bar (could be floating or tie wrapped) with ground wires going to it - tighten them all and trace the primary to the firewall and tighten that also.
After assembly it may take a couple of starts to get things coordinated again - but your problems may well go away.
I had air pressure trouble- the gauge would bounce from 125 to 70 and back up while the primary tank gauge would stay at 125. No way could air escape and then pressurize as quickly as that needle moved. So, it was an electrical problem that was solved by the procedure I outlined.
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2008 Phaeton 36QSH, Safe-t-Plus, Quadra Bigfoot
2017 Jeep Cherokee Trailhawk w/ flat tow wiring mod.
Blue ox, BrakeMaster + BrakeAway, diode lights and charge.
Could be a (reduced) voltage problem; we had the same issue on an older Freightliner chassis w/Cummins 5.9 and Allison 3000.
While you have things apart and after cleaning connections (I recommend Deox-it), if the problem persists use a multimemter to check the idle voltage on as many dash elements as possible. Look for significantly reduced voltage (e.g. 8-9 volts or less instead of 12+). If you see that, then start back tracking the circuit, looking for damage, loose connections, etc.
Our problem turned out to be damage to an electrical loom on the chassis, probably caused by road debris.
Over the past 25 years Freightliner has used three different dash gauge/ light bar/warning systems.
Up to 2004 the system carried the VDC acronym .
From 2004 to 2007 , MMDC
After 2007 the LBCU .
By your chassis year your system should be the MMDC. So you'll be getting some info that may not apply to your system .
By all means clean your connections , but if your're still having issues , call Freightliners free help line with your chassis serial number and ask for paperwork for testing your MMDC dash system.
I have the testing info for the VDC and the LBCU , but not the MMDC , otherwise I'd share it now.
1-800-385-4357
Over the past 25 years Freightliner has used three different dash gauge/ light bar/warning systems.
Up to 2004 the system carried the VDC acronym .
From 2004 to 2007 , MMDC
After 2007 the LBCU .
By your chassis year your system should be the MMDC. So you'll be getting some info that may not apply to your system .
By all means clean your connections , but if your're still having issues , call Freightliners free help line with your chassis serial number and ask for paperwork for testing your MMDC dash system.
I have the testing info for the VDC and the LBCU , but not the MMDC , otherwise I'd share it now.
1-800-385-4357
I agree Skip - model years changes can be notorious for misleading folks. If I recall, I seem to remember reading that the MMDC had the daisy chain wiring problems and may have had black wires? Freightliner had gone through a period where they were simply sending out new wiring sets.
Thanks for helping to caution OP regarding the exactness of advice from different model year rigs...
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2008 Phaeton 36QSH, Safe-t-Plus, Quadra Bigfoot
2017 Jeep Cherokee Trailhawk w/ flat tow wiring mod.
Blue ox, BrakeMaster + BrakeAway, diode lights and charge.
I cleaned all the terminals with CRC contact cleaner. Removed the positive and negative posts under the dash and on the front side of the fire wall. Drove to June Lake this past week, and it worked fine for about an hour then started to drop in indicated speed. Also the tach now reads about 500-600 rpm low. What is interesting is that if I stop the vehicle, it will work fine again for about 15-30 minutes. If I replace the MMDC, does it need to be reprogrammed, or is it a direct plug and play?
Just an FYI they have changed out the white cables to a heavier black. You can purchase direct from Freightliner. The computer mod has been replaced 5 times and I still don’t get a accurate odometer reading. Want to go to Gaffney but COVID has really messed up the plans. 2007 Journey 34H
So I took a chance and replaced the MMDC Medallian board. Set me back $800. Didn’t really fix the problem, although it acts different. When I first started driving, everything seemed fine. Then speedo started to decline until it hit zero. Stopped for a bathroom break, and it was fine. Next day, speedo started out fine then started to read higher than my gps. Also, tach was about 1,000 rpm low. Stopped for fuel and then both were fine for remaining hours drive. Very strange. The search goes on.
Linear Mode
