RABS problems
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Joined: Mar 2008
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From: douglasville
RABS problems
I just bought an 87 f250 with a 6.9 diesel and a c6 and now the rabs light and the brake light are both on all the time. I can stop and shut off the engine and when I start it the lights are off but as soon as I put my foot on the brake pedal both lights come on and stay on also the brake pedal is really hard like there is no power assist but the booster is working the truck does stop real good but its bothering me and I have no info as to how to retrieve the codes or what the codes mean! any help would be much appreciated. Thanks!
Elder User
Joined: Sep 2013
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hmmm well how do u know your brake booster works ? and on theses simple brake systems u really dont need to know the exact codes cus there really are none. But things to check would be brake fluid level and condition of fluid because they can stick ur level sensor and make it think its low. And if those check out ok then u can check ur rear speed sensor on ur diff. Honestly if ur truck stops good then i wouldnt worry about it its a very simple set up
i ain't rite
Joined: Mar 2005
Posts: 65,564
Likes: 5,601
From: Marlboro Mental Hospital.
your problem is most likely a dead vacuum pump.
diesels do not have intake vacuum like gas engines do, so they have a vacuum pump on the front of the engine to make vacuum for the brake booster to work. hard pedal is a sign of no vacuum to the booster.
diesels do not have intake vacuum like gas engines do, so they have a vacuum pump on the front of the engine to make vacuum for the brake booster to work. hard pedal is a sign of no vacuum to the booster.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
To retrieve codes there should be a black/orange wire under the dash that can be grounded, and then the key cycled to flash codes out on the RABS light.
I don't know enough about the specifics of a diesel wiring harness to tell you exactly where this wire is.
I don't know enough about the specifics of a diesel wiring harness to tell you exactly where this wire is.
i ain't rite
Joined: Mar 2005
Posts: 65,564
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From: Marlboro Mental Hospital.
you can not retrieve codes on a diesel with a C-6 or manual trans, because there is no computer to store them .
the only things that will activate the check engine light are low oil pressure or high coolant temps.
the only things that will activate the check engine light are low oil pressure or high coolant temps.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 40
From: EXTREME southwest CT
It's not a PCM, It's the RABS computer and entirely independent of any engine management.
It is the RABS light and the brake failure lights that are on...
It is the RABS light that flashes when you ground the wire and turn the key.
Do you think I have an engine computer in my DSII truck Tom?
I understand what you're saying about a problem vacuum pump causing a hard pedal.
Hydroboost is always an option.
It is the RABS light and the brake failure lights that are on...
It is the RABS light that flashes when you ground the wire and turn the key.
Do you think I have an engine computer in my DSII truck Tom?
I understand what you're saying about a problem vacuum pump causing a hard pedal.
Hydroboost is always an option.
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Joined: Mar 2008
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From: douglasville
I have fixed it! I already had a new vacuum pump and a new master cylinder already and I found the wire that is supposed to be grounded to check the codes but when I grounded it all the light would do is come on and stay on and go off only when the ground jumper was removed so I went a little further and checked the fluid pressure at the rear brakes and there was none and not much at the RABS valve so I borrowed the RABS valve off my 94 F350 and bled the brakes. now I have no abs light and the brakes work perfect so now I have to get a new one for the 94
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i ain't rite
Joined: Mar 2005
Posts: 65,564
Likes: 5,601
From: Marlboro Mental Hospital.
It's not a PCM, It's the RABS computer and entirely independent of any engine management.
It is the RABS light and the brake failure lights that are on...
It is the RABS light that flashes when you ground the wire and turn the key.
Do you think I have an engine computer in my DSII truck Tom?
I understand what you're saying about a problem vacuum pump causing a hard pedal.
Hydroboost is always an option.
It is the RABS light and the brake failure lights that are on...
It is the RABS light that flashes when you ground the wire and turn the key.
Do you think I have an engine computer in my DSII truck Tom?
I understand what you're saying about a problem vacuum pump causing a hard pedal.
Hydroboost is always an option.
but i do know there is no way to pull codes from your 87 with a 460 either.
i can not see a 87 diesel having a ABS computer, because my 88 diesel does not have one. all it has is the valve in the frame that has been bypassed since the truck was a few months old.
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From: douglasville
no idea Jim, i don't know what a DSII truck is.
but i do know there is no way to pull codes from your 87 with a 460 either.
i can not see a 87 diesel having a ABS computer, because my 88 diesel does not have one. all it has is the valve in the frame that has been bypassed since the truck was a few months old.
but i do know there is no way to pull codes from your 87 with a 460 either.
i can not see a 87 diesel having a ABS computer, because my 88 diesel does not have one. all it has is the valve in the frame that has been bypassed since the truck was a few months old.
i ain't rite
Joined: Mar 2005
Posts: 65,564
Likes: 5,601
From: Marlboro Mental Hospital.
unscrewed the lines going into and out of the valve, and put a short line between them.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 40
From: EXTREME southwest CT
no idea Jim, i don't know what a DSII truck is.
but i do know there is no way to pull codes from your 87 with a 460 either.
i can not see a 87 diesel having a ABS computer, because my 88 diesel does not have one. all it has is the valve in the frame that has been bypassed since the truck was a few months old.
but i do know there is no way to pull codes from your 87 with a 460 either.
i can not see a 87 diesel having a ABS computer, because my 88 diesel does not have one. all it has is the valve in the frame that has been bypassed since the truck was a few months old.
I CAN pull codes from my RABS computer Tom.
It's an entirely separate system from any engine management.
What do you think feeds a signal to the plug on the RABS valve located on the frame rail???
What do you think lights the bulb up on the cluster?
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
unscrewed the lines going into and out of the valve, and put a short line between them.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
The abs valve has four wires going to it.
Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
unscrewed the lines going into and out of the valve, and put a short line between them.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
my abs valve had one wire on it that went to the light. the light would come on if there was a loss of pressure in the rear brake circuit.
it was about as basic of a circuit as there was.
You'll find that RABS, or ANY antiskid brake system for that matter, will always have an electronic controller as well as it's own warning light separate from the red brake warning light.