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willism
Senior Member

United States
142 Posts

Posted - 09/19/2013 :  09:58:21 AM  Show Profile  Visit willism's Homepage  Reply with Quote
Got a 09 c2 lift bus.. The issue is I cannot get the brakes to release it just dumps the air. Now when the parking brake is applied and shut the bus off it gives you that error steady buzzer that tells you your parking brake is released and with the bus on the park brake light is not on with the park brake applied. I cannot get the lift to work either im assuming the same error that tells me the park brake is not applied is causing the lift to not work not that the lift is causing the issue. Anyone got any ideas I checked all the connectors on the chassis module they looked ok.I hooked up service link and had no active faults only odd thing was when i hooked it up the abs light came on and wont go off and according to the wabco software I have a abs light on but no faults. Im trying to locate the air manifold unit module but not having any luck. Thanks

Bus Tech II
Senior Member

108 Posts

Posted - 09/19/2013 :  10:32:27 AM  Show Profile  Visit Bus Tech II's Homepage  Reply with Quote
Is the lift switch on when trying to release park brake? The lift switch must be off to release brake. If thats ok then you probably have an issue with the AMU ( air management unit)
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tigger2
Advanced Member

USA
284 Posts

Posted - 09/19/2013 :  10:39:00 AM  Show Profile  Reply with Quote
The AMU or air management unit is right behind the transmission just above the ujoint as is the norm. look for the valve section (module) with the yellow 1/4" air line that is the parking brake section if the drl(daytime running lghts) don't come on with the brakes released the modual is bad. Did your Thomas dealer give you access to My TBB online? You can look up wiring and locations on there. The lift interlocks must see parking brake or the lift wont work and the brakes wont release. Also when you do release the brakes you need to make a full brake app as you push in the yellow valve or it will dump all the air, and hold your foot on the brakes untill the drl lights come on just to be sure.
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willism
Senior Member

United States
142 Posts

Posted - 09/19/2013 :  11:07:24 AM  Show Profile  Visit willism's Homepage  Reply with Quote
Knew about the lift switch the drivers hate that feature and get messed up all the time. No the drl's do not come on. Only have a few c2's and not to familiar with tbb but i do have access to it ill fumble through it after lunch. Have to chip away all the undercoating they sprayed this one down really well. Thanks for the help guys.
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willism
Senior Member

United States
142 Posts

Posted - 09/26/2013 :  04:43:18 AM  Show Profile  Visit willism's Homepage  Reply with Quote
Ok finally got the amu in that was suggested and changed its still doing the same thing any suggestions.. thanks
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Bus Tech II
Senior Member

108 Posts

Posted - 09/26/2013 :  05:20:50 AM  Show Profile  Visit Bus Tech II's Homepage  Reply with Quote
HMMMMM. I was almost positive that would be your problem. The only other common thing i can think of it the wiring harness chaffe near the head of the air compressor.
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willism
Senior Member

United States
142 Posts

Posted - 09/26/2013 :  06:19:05 AM  Show Profile  Visit willism's Homepage  Reply with Quote
Well after sitting over night everything will work once but after you shut it off and turn it back on the problem comes back and does it the rest of the day so im at a loss. Ill go double check the harness. Thx

Could not find anything rubbing there or anywhere else except a ac line i tied up a little bit better

Edited by - willism on 09/26/2013 07:27:45 AM
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Bus Tech II
Senior Member

108 Posts

Posted - 09/26/2013 :  1:03:44 PM  Show Profile  Visit Bus Tech II's Homepage  Reply with Quote
What part of the AMU did you replace? Was it the part that has several ports in it or just the single port?

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mbfromnc
New Member

7 Posts

Posted - 09/26/2013 :  1:55:48 PM  Show Profile  Visit mbfromnc's Homepage  Reply with Quote
Repin connector c4 at the chassis module. You can clean and spread pins for a temp fix
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willism
Senior Member

United States
142 Posts

Posted - 09/27/2013 :  03:54:17 AM  Show Profile  Visit willism's Homepage  Reply with Quote
The park brake amu single 1/4 inch line port with 1 connector. I assume c4 connector is the one that carries the red/white wire from the park brake amu right?
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willism
Senior Member

United States
142 Posts

Posted - 10/09/2013 :  07:27:21 AM  Show Profile  Visit willism's Homepage  Reply with Quote
Finally got it fixed the chassis hub module was bad. just fyi
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Bassman
Top Member

USA
511 Posts

Posted - 10/10/2013 :  07:17:26 AM  Show Profile  Reply with Quote
FYI guys....our buses have two Chassis Hub Modules side by side. For diagnostic purposes, you can switch the two modules and see if it fixes your problem. If (with emphasis on the if) the other Chassis Hub Module doesn't use the section that happens to be bad, you can leave it that way! (This worked for us on one bus and got it right back on the road).
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