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sclord2002

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.

 

Nigel

Edited by Nigel

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Hi Charlie,

Please keep us update on what you found and how you went and made the repairs. Curious minds need to know. It almost sounds like you might need to remove the left bottom part of the dash to get to where the sensor could be.

Best of luck on the repairs,
Al

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Not 100% sure on Volvo's, but it should be inside the cab. Follow the line back from the gauge on the tank that's acting up. It should come to a manifold, follow the 2nd 1/4" line to the sensor.

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Charlie, pressing the "ESC" button on the wiper stalk should temporarily silence the warning buzzer.  Probably too late to bring that up since you are back home.  I can't imagine driving 70 miles with that thing screaming - it would make one crazy!

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Randy;

It is, after all, Charlie the Tool Man. My advice for him is to start with a large hammer and work on getting the purge valve(s) to work properly. If that doesn't work, get drunk.

See ya'll  at the rally

Paul

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22 hours ago, adept99 said:

Randy;

It is, after all, Charlie the Tool Man. My advice for him is to start with a large hammer and work on getting the purge valve(s) to work properly. If that doesn't work, get drunk.

See ya'll  at the rally

Paul

LOL.    Al

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18 hours ago, sclord2002 said:

Al,  I have ordered the sensor.

Hi Charlie, good to know that you are on top of it. I think you will have a story this coming spring.

Al

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2 hours ago, sclord2002 said:

Replaced air pressure sensor.....resolved problem.  Darryl was right on target.  Thanks !!   Charlie

Hi Charlie,

Was the part located inside the truck on the left side of the dash ? Curious minds need to know. Good to hear to the is repaired.

Al

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14 hours ago, sclord2002 said:

Replaced air pressure sensor.....resolved problem.  Darryl was right on target.  Thanks !!   Charlie

Sometimes I just get lucky. 

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So what are we looking at in the Volvo pic above?  Brake light switch on the top?  Park brake switch on the left?  Primary and secondary transducers down below?  They case ground these things with that ring terminal above?  Or is that something else?

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2 hours ago, Darryl&Rita said:

But what does what? 

We keep forgetting, you Kenworth guys don't have the Secret Decoder Ring.😋

That doesn't look like the one in our truck.  Plus, the one above is cleaner.

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