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Air brake issue


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While heading home form Charleston,SC, in my 2006 Volvo 780, my front air tank gauge dropped to zero, the warning sounded and the display said low system air pressure.  i immediately pulled over and began to ponder the situation. I left the truck running and walked around the truck trying to listen for an air leak....no luck.  I looked under the hood and every thing looked ok. I then shut the truck down and listened for leaks...no good, again. I pulled the moisture drain cable on the front and rear tanks and both had pressure and no moisture, The rear tank pressure gauge was normal and cycling normally. I then proceeded to cycle the key off and on to observe the gauge check process.  After cycling the key 4 times the front tank air gauge displayed normal pressure and cycled normally as the air governor called for air. I drove off and after about 10 miles, the front tank gauge dropprd to zero just as before, but this time there was not a good shoulder  to pull off on, so I nervously continued on, expecting some kind of negative brake action.....nothing occured with the brakes but the alarm is not a good thing to listen to. I pulled into a truck stop and cycled the key several more times and the front air tank gauge started showing some pressure but not as much as the rear tank. I asked a mechanic at the truck stop about it and he said it sounded like a flaky pressure transducer. I continued the remaining 70 miles home with the rear tank gauge normal and the front tank gauge reading about half of that.  Time and weather are preventing me from attacking the problem but I can't stop thinking about it. I would be grateful if someone with more air brake knowledge than I have would share their thoughts on this.  Thanks in advance.    Charlie

Edited by sclord2002
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I agree with Darryl.  Had a similar situation except mine acted up on a start from cold.  Front gauge wouldn’t climb from zero and alarm wouldn’t stop but lots of air in tank.  The sensor is inside the cab in front of your left foot where the air lines pass through.  There are a couple there and I think I disconnected one at a time, applied brakes and checked gauges to figure out which one it was.



Edited by Nigel
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