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Discussion Starter #1
My brakes power assist is not working, push hard, brakes little. I pulled a code with my test light since a code reader does not work. The code was 4 sets of 9 flashes. 9999 What is this code?
 

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The flash-out code format repeats the code 4 times so your code is 9, not 9999. Code 9 means high resistance in the rear wheel speed sensor/circuits on the rear axle. This would have nothing to do with your lack of power assist though. Just to verify what you have, is this a vacuum or Hydro-Boost system?


Ford Motor Company said:
9.4 CHECK FOR OPEN SENSOR
Verify ohmmeter is on 20K ohm scale.
Measure resistance between RABS sensor Pins A and B.
Is resistance less than 2500 ohms?
 

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Discussion Starter #3 (Edited)
Just to verify what you have, is this a vacuum or Hydro-Boost system?
I don't know. How can I tell? I do have a pump looking thing that the belt runs that sits right next to the oil fill spout that has a hose that connects to the vacuum manifold from which a hose runs to the power booster. I did check the hose that connects to the power booster yesterday for vacuum with my finger. The vacuum was almost not detectable but there was a slight vacuum. I don't know how much vacuum is needed.
 

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Discussion Starter #4

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A Hydro-Boost system uses power steering fluid as a booster which was commonly found on F350/450 dual rear wheel applications but there were some weird ones that had it. I was pretty sure your truck has a vacuum booster but we don't want to assume. Your truck should have a low vacuum sensor connected somewhere between the pump and the vacuum booster... cant always be sure it has not been removed or is non-functioning. For your lack of power brake assist make a visual inspection for leaks and obvious damage. Next step would be to verify vacuum which should be in the 18" to 22" range. If present and working, the low vacuum warning switch should turn on the red brake warning indicator on the instrument cluster when vacuum drops below 10" for more than 7 seconds.
 

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Discussion Starter #6
Yes, that light was on yesterday.
 

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I would say that your vacuum pump is shot. Either that or you have a massive vacuum leak.
 

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Discussion Starter #8
I would say that your vacuum pump is shot. Either that or you have a massive vacuum leak.
You are right. After I disconnected the pump hose from the vacuum manifold and ran it directly to the booster, it worked fine. :smile2: What else hooks into the vacuum on these trucks?
 

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Follow the main hose from the vacuum pump, on the driver's side fender well there is a manifold/check valve check the manifold for leaks, and also, look at the check valve to see if it works. From there, look at all of the lines running from the manifold, check for leaks.
 

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Discussion Starter #11
Turns out, the hose from the vacuum pump to the manifold had a hole in it. Replaced it and the vacuum is excellent. :)
 
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