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Old 09-20-2021, 07:21 PM   #1
Skoolie
 
Join Date: Jun 2015
Location: Toledo OH
Posts: 224
Year: 2006
Coachwork: Thomas
Chassis: MVP-EF
Engine: Cat C7 + Allison MD3060
Thomas bus - all gauges don't work/read incorrectly only when engine is on

Hi guys, here's yet another dash gauge related issue, but this one is a little different.


So when I first got my bus, all the dash gauges worked fine, EXCEPT the tachometer. When you put the key in and turned it to ON before starting, the gauges would all sweep and return to zero (except the tach), and the odometer would show 2_09, then would show the battery voltage. When you started the engine and got things running, again everything except the tach worked normally.


I took the bus to a mechanic to have the air dryer and main air line replaced, and in the process they found that my low air sensors that feed the low air alarm buzzer in the dash were bad, so they replaced those sensors (they were literally broken). However, now the gauges do something really interesting:
  1. Turn key to ON, all gauges except tach sweep, odometer shows 2_09, everything goes back to zero and life is good.
  2. Start engine, none of the gauges do anything. Every segment on the digital tach lights up, and the BRAKE and LOW AIR lights stay on (but no buzzers). I don't get a speedo, coolant, battery, fuel, oil pressure...nothing. BUT my BlueFire is still able to read those values just fine.
  3. While driving, occasionally the warning lights on the gauges themselves will light up and I'll hear the buzzer, but the gauges never read an actual value, and then everything goes dark again.
To me, this doesn't sound like a grounding issue because I don't know why a lack of ground would make the gauges work when the engine is off, but maybe there's something obvious about this particular situation that might help provide a tip to me. I'd appreciate your thoughts!

dbsoundman is offline   Reply With Quote
Old 09-20-2021, 07:59 PM   #2
Skoolie
 
Join Date: Jun 2015
Location: Toledo OH
Posts: 224
Year: 2006
Coachwork: Thomas
Chassis: MVP-EF
Engine: Cat C7 + Allison MD3060
Just noticed something else interesting...the backlight for the speedometer and the fuel gauge won't turn off! This is with the key out/off, engine off...for several hours already.
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