I have a bus that has the red light for service barking brake staying on after releasing the p/b. I installed a new cable as old one was getting grouchy about releasing. Everything is adjusted correctly (stroke to minimal). Are these things that touchy about travel distances? Where is a happy medium then??
I am leaning toward a faulty travel switch (MGM #9051001) or wiring to the brake ECU as I have no daytime running lights on/off while cycling the park brake switch either.
Anyone have any testing info on the travel switch? What does it sense inside the SAHR canister? I have dug around on the net for info but haven't found much more than a peep about the switch or the SAHR assy.
Make, model VIN? If it is a Navistar this system is a PIA. Have 2 ambulances with this system. Flashing the body computer will shut it up for a while. Without the body computer software this is tough to troubleshoot. Have tangled mwith 7 or 8 of these over the years. Maybe once it was travel switch. The software has to see 2 signals. One from the travel switch, the other from the park brake switch on the dash. It then processes these signals. If the software is glitchy the light comes on.
Make, model VIN? If it is a Navistar this system is a PIA. Have 2 ambulances with this system. Flashing the body computer will shut it up for a while. Without the body computer software this is tough to troubleshoot. Have tangled mwith 7 or 8 of these over the years. Maybe once it was travel switch. The software has to see 2 signals. One from the travel switch, the other from the park brake switch on the dash. It then processes these signals. If the software is glitchy the light comes on.
What follows is how this works on a truck. I'm pretty sure it is true for buses. The ABS and Hydraulic Power Brake (HPB) system are Meritor and usually the park brake system are all controlled by the Meritor ECU. On a NAV, for reasons unknown the park brake warning and controls go thru the chassis body controller. To make it even more confusing the fault code layout is the same as Meritor's except the specific codes won't show up in the Meritor manual. I don't think they even show up in the Meritor software. They are found with Diamond Logic Builder (DLB) NAV's body computer program. Or the can be pulled from the dash. It is a hair pulling pain. As I mentioned before reflashing the body computer makes it go away IF you verify that both signals are getting to the body control. One from the travel switch and the other from the dash park brake switch.
What follows is how this works on a truck. I'm pretty sure it is true for buses. The ABS and Hydraulic Power Brake (HPB) system are Meritor and usually the park brake system are all controlled by the Meritor ECU. On a NAV, for reasons unknown the park brake warning and controls go thru the chassis body controller. To make it even more confusing the fault code layout is the same as Meritor's except the specific codes won't show up in the Meritor manual. I don't think they even show up in the Meritor software. They are found with Diamond Logic Builder (DLB) NAV's body computer program. Or the can be pulled from the dash. It is a hair pulling pain. As I mentioned before reflashing the body computer makes it go away IF you verify that both signals are getting to the body control. One from the travel switch and the other from the dash park brake switch.
I took a look at your bus by VIN. It is different from truck. All your signals go to the ABS computer which is better. I would check connections at the travel switch especially and the solenoid for the canister. There have been some problems with pushed back terminals. The switch is a Hall effect and is very reliable. The wiring at the plug not so much. Were you able to get any codes out of it? The ABS computer wants to see signals from the park brake switch on the dash and the travel sensor at the same time. If it sees one and not the other or there is to big of a lag it will set a code and turn on the light. HTH
More Wabco HPB brake system fun.....
Posted - 02/06/2020 : 07:02:39 AM
