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Old 01-28-2012, 10:16 AM   #1
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Air Brake Warning

Hello all, newbie to the forum here. I have been trying to get my father-in-laws 2001 Monaco Diplomat Le up and running again. After setting up for 3 years, I have repaired wires that the field mice used for lunch and had the ECU repaired. The only issue that I have left is with the air brakes. The coach has no warnings going off and no lights on dash or anywhere else. My problem is that as soon as you press the brake pedal, a warning bell goes off. It appears to be the same one that sounds as the air pressure is building up when I start it. As soon as the pressure is up, it goes off until I press the brake. As soon as I release the brake, it stops.

Any suggestions.


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Old 01-28-2012, 10:22 AM   #2
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Hi and welcome to the forum! I'm sure some of our experts will be along shortly to help out with your question.

We're glad you found us.


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Old 01-28-2012, 10:27 AM   #3
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What are the air pressure readings on the dash gauges when this is occurring? Do the warnings sound then go off from start-up (with air low)?
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Old 01-28-2012, 10:44 AM   #4
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Air pressure builds up to 120 and shuts off initial warnings on start-up.
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Old 01-28-2012, 10:48 AM   #5
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Sounds like one of the air brake canisters is leaking when you press the brake pedal. Have someone press the brakes and walk around the coach and listen for leaks.
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Old 01-28-2012, 10:48 AM   #6
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Welcome to the forum. Hope you enjoy your time here. Can't answer your question but I'm sure someone will be along to help you out. Hope you enjoy the coach and all your travels. Be safe and Happy Motoring!!!
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Old 01-28-2012, 10:54 AM   #7
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My father in law did say that he had a blow out that damaged the valve to one of the rear airbags. The coach also looses air in that bag overnight and is leaning the next morning. Could that be what is happening? The warning is going off when I press the pedal because air is escaping through that damaged valve on the airbag?
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Old 01-28-2012, 10:57 AM   #8
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When you press on the brake pedal does the 120 PSI shown on the gauges drop below 60 PSI right away??
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Old 01-28-2012, 11:01 AM   #9
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Nope, It will drop, but not below 60. It appears to be working correctly. It will drop and rebuild to 120 pretty quickly.
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Old 01-28-2012, 12:14 PM   #10
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When you push the brake peddle do you have the parking brake released. If so the warning buzzer will sound if the transmission is not in gear. Also could be a jacks down warning.
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Old 01-28-2012, 01:22 PM   #11
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Originally Posted by slickest1 View Post
When you push the brake peddle do you have the parking brake released. If so the warning buzzer will sound if the transmission is not in gear. Also could be a jacks down warning.
Jacks are up, parking brake is released. Coach is in drive going down the road. Brakes are working. As soon as a press the brake, the warning signal goes off. As soon as a take my foot off the brake it stops.
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Old 01-28-2012, 01:50 PM   #12
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If you arent hearing a big air loss when pedal is depressed I would be a little suspicious that you may still have wiring to repair. Kinda scary when mice start making your home theirs! The other thing is what did you have to have repaired on ECM? Maybe there is a fault in the ECM. I'd be tempted to take to an authorized centre and pay whatever it costs to have them hook up to computer. They may be able to see a fault code or alarm triggered once you push brake pedal. Jon
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Old 01-28-2012, 02:17 PM   #13
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Try running this test on your air brakes and air system and see if you hold the pressures for the required time.

Brake System Check Procedure

(Note- Damage can occur to your service brakes if pedal is pumped hard while Park/Emergency brake is engaged.)
  • Be sure rig is on level ground and/or use chalks
  • Start the engine. Let the air pressure build up until the governor activates the air compressor cut-out release of air at about 120-130 psi.

Check the Air Compressor Cut-Out and Cut-In Function
  • Release the emergency/parking brake.
  • Press the brake pedal several times until you see the needle drop to around 85-90 psi.
At that point the governor should activate the air compressor cut-in and the pressure should build back to 100 psi in about 45 seconds.
Allow the pressure to build to cut-out at about 120-130 psi.

Check for Air Leaks
  • Shut off the engine, but leave the ignition in the "on" position.
Watch the gauge for one minute - there shouldn't be more than a 2 psi drop in pressure. (This checks for leaks from the air compressor to the tanks and the one-way check valves.)
  • Press the service brake (brake pedal) and hold it down for one minute. There should be no more than a 3 psi drop in pressure. (This checks for leaks with the system under pressure: the air lines, one-way check valves, and Diaphragms.)

Check Audio and Visual Low Air Pressure Alarms/ Adjust Auto Slack Adjusters
  • Turn the engine back on and let the compressor build pressure to the air compressor cut-out.
Turn the engine off but leave the ignition switch on.
Smoothly pump the service brake pedal until the low air warning light and buzzer activate. Devices must activate at not less than 60 psi.

Check the Emergency/Parking brake Function
  • Continue to pump the service brake pedal until the emergency brake pops out automatically. Application should occur between 20-45 psi.
  • Start the engine and allow the air compressor to reach cut-out level.
Remove any wheel chalks.
Shift into gear.
Apply your accelerator, but not over 1000 RPM.
Your Rig should not move.

NOTE: Slack Adjustment

Ensure reservoir air pressure is above 90 lbs on both air tanks and make a FULL brake application and release (Hard application to the floor). Repeat this process 6 times. (These brake applications will be adequate to cause the automatic slack adjusters to adjust)

Note: A light brake application will not cause the adjustment
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Old 01-28-2012, 02:19 PM   #14
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The Allison Transmission ECU was repaired due to the fact that the shifter was not lighting up. They said that it wasnt powering up and so he repaired that. Dont know if there would be any connection with the brakes or not. If there is, I could get him to test again.

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