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 brake pressure light coming on- why??
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whe8913
Advanced Member

United States
301 Posts

Posted - 06/07/2011 :  10:14:23 AM  Show Profile  Reply with Quote
Maybe someone can help me with this gremlin!

I have an 01 with the T444E- hydraulic brakes with air applied park brake. Everything checks out (no leaks, fluid full in master cylinder and pwr. steering) and the brake pressure light and buzzer come on. Any thoughts? I have unplugged the sensor on the master cylinder and cleaned it, and it still persists.

slippert
Advanced Member

USA
402 Posts

Posted - 06/07/2011 :  11:16:31 AM  Show Profile  Reply with Quote
quote:
Originally posted by whe8913

Maybe someone can help me with this gremlin!

I have an 01 with the T444E- hydraulic brakes with air applied park brake. Everything checks out (no leaks, fluid full in master cylinder and pwr. steering) and the brake pressure light and buzzer come on. Any thoughts? I have unplugged the sensor on the master cylinder and cleaned it, and it still persists.



There are a number of things that can cause your problem if I remember correctly? Not just the switch on master cyl, has been a few yrs since last hyd brake bus left here. seems like I found anything from bad grounds at the brake lights, which was common, bad brake pedal switches, switches on the hyd brake booster, monitor module under dash, low pump pressure in system, bad connections and/or wiring.

I believe the light and buzzer get there grd from the monitor module under dash. 90t and 90s should be the wire numbers. 90m should be a grd feed from motor relay that gets it grd from press diff switch and flow switch on booster. all three of them also go to the monitor module. I might be able to e-mail you a wiring diagram out of a book if you want

it seems like there was a diode kit IH made for just such an emergency but i don't remember part #


I don't know about anybody else but what you are talking about was a pretty common problem here when everything was hyd brakes

Does the problem go away for awhile, if you pull over and shut bus down then restart? is this your personal bus ? or a school bus


Edited by - slippert on 06/08/2011 04:35:42 AM
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whe8913
Advanced Member

United States
301 Posts

Posted - 06/07/2011 :  10:00:30 PM  Show Profile  Reply with Quote
Yes, the problem goes away for a while when the bus is shut down and restarted. The timing varies- sometimes it's for a few miles, other times it's for a few seconds. The ironic thing is that I hit a horrible bump in the road yesterday, and it went away for a bit after that. This is a bus that my church has; it's been a decent bus, but not without its own share of glitches- mostly electronic related. The only v-8 diesel that they have. The rest are DT's or 5.9's. It "eats" cam position sensors like candy too. It's only got 52,000 miles on it, so we'll be hanging onto it for awhile longer.
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Bassman
Top Member

USA
516 Posts

Posted - 06/08/2011 :  03:00:13 AM  Show Profile  Reply with Quote
9 times out of ten, it is a bad ground on a rear brake/parking light, or a bad brakelight bulb. Do your self a favor and replace all 4 bulbs and clean up all taillight grounds first and odds are you'll fix it.
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slippert
Advanced Member

USA
402 Posts

Posted - 06/08/2011 :  04:37:56 AM  Show Profile  Reply with Quote
so, ck the bulbs and grounds at tail/brake lights first. chances are if it goes away with shutdown it's connection problems.
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whe8913
Advanced Member

United States
301 Posts

Posted - 06/08/2011 :  7:35:14 PM  Show Profile  Reply with Quote
Concerning the S/T/T lights, I converted them last summer to LED. Would that have any impact, voltage-wise, etc? Granted, they've been in use a year, and this is just now starting to occur.
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Bassman
Top Member

USA
516 Posts

Posted - 06/09/2011 :  03:14:40 AM  Show Profile  Reply with Quote
It's been a while since I have worked on this part of the system but...there is a module under the dash on the firewall. Among other things, it monitors the brakelights/brake boost operation. It must see voltage from the pedal switch on two of the wires at the same time...brakelights and brake boost. If the taillight ground is bad or if the filament is crossed either externally or in the base of the bulb, the voltage crossing from the parking light circuit is (by a backfeed up the brakelight wire)read by the module as if the brakes are applied. But since it doesn't see the voltage coming from the pedal to the brake booster at the same time, it thinks there is a problem. Try duplicating your problem with the parking lights off and see if it doesn't fix the problem. IH made an add-on diode kit to prevent this, but in a properly working system, they aren't necessary. I know that is a little generic in description, but that's how the error usually occurs. I am not well versed in the LED units but if it worked for a year, it's not in the design, but maybe a bad unit or ground. Do you have brakelights from a sister bus to swap?
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Harrison Fire
Senior Member

United States
175 Posts

Posted - 06/10/2011 :  11:46:27 AM  Show Profile  Reply with Quote
I posted part of what follows a while back.
My juice brake Navistar buses are older (99 down) with a lever parking brake so this may not apply to your situation.
HF

"This post bugged me since I have had to deal with a Hydromax as well.
A while ago,I searched online for, and found, then printed a handy, dandy manual for this puzzling setup.
Had to search 2 times today using different wording to find it again.
My suggestion is to print it out.
I have looked at it several times since I made a copy.
HF

http://rb-kwin.bosch.com/pool/usa/pdfs/HydroMax_Hydraulic_Brake_Booster_Manual.pdf "



My Fleet? (6) 93/99 IH 3800 Thomas and Blue Bird, Hydraulic Brakes, Manual and Auto Trans, (10) 00/06 FS65 Thomas Air Brake and Auto Trans, (2) 06 C2 Thomas and (2) 09/10 IC CE 300, Plus 3 more from another District
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C.HARDY
Advanced Member

354 Posts

Posted - 06/14/2011 :  6:08:59 PM  Show Profile  Click to see C.HARDY's MSN Messenger address  Reply with Quote
I had same situation. All electrical checked out. I removed the plug from the mastercylinder and started the bus for just a second. It blew out some fluid and maybe some debris because it never gave any more problems. Just something to think about.

"Hardybusman"
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willism
Senior Member

United States
143 Posts

Posted - 06/15/2011 :  1:25:17 PM  Show Profile  Visit willism's Homepage  Reply with Quote
We have had a few 02 IHC Hyd buses that the relay on the left side behind the power panel access door was was intermittent. Should be 3 small relays upper left. Hope this might help
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Trailboss
Senior Member

United States
149 Posts

Posted - 07/05/2011 :  03:49:42 AM  Show Profile  Reply with Quote
Does this bus have two brake light switches at the brake peddle. They must be timed to work at the same time.This will also cause the brake pressure light to come on.I used two test lights and ajusted switches so the lights came on at the same time.
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Denis Martin
New Member

1 Posts

Posted - 05/03/2013 :  9:35:44 PM  Show Profile  Visit Denis Martin's Homepage  Reply with Quote
Hi I have a 2001 ih 3800 school bus.The brake pressure buster is on and the hydrolic motor won't run with engine off.Ive had this problem on some of my other busses usually change the relay by the master cyl and the square box on the firewall inside the cab behind the brake gas pedals.Problem gone not this time I've even changed some of he relays near the busser itself?i don't have a pressure problem but I don't get what else to look at ?Brake switch ?Brake light bulbs?
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Bassman
Top Member

USA
516 Posts

Posted - 05/06/2013 :  04:16:11 AM  Show Profile  Reply with Quote
Also check taillight grounds!
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