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Andy, Truck Diagnostic Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 1675
Experience:  International and Isuzu trucks , International, Maxxforce, Cummins and Isuzu engines, Diagnostic and electrical troubleshooting specialist , Hvac and truck /trailer refrigeration troubleshooter
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I have a 98 IH 4700 t444e and the brake pressure light is

Customer Question

I have a 98 IH 4700 t444e and the brake pressure light is staying on in the truck and the motor on the hydro boost is staying running with the ignition on the on position or with the motor running. I didn't have power steering so I changed the power steering pump and the hydro boost and the master cylinder, now I have power steering, but still have a problem with the brake pressure light and motor constantly running. The only thing I haven't replaced under the hood was the relay and the electric motor on the hydro boost. The only way the motor will cut off on the hydro boost is if I unplug the sensor on the master cylinder.
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Andy replied 1 year ago.

Ok have you replace the flow switch ?

Customer: replied 1 year ago.
the master cylinder has a new switch and the hydro boost has a new switch. Is there another one that I am missing?
Expert:  Andy replied 1 year ago.

There are diodes, a relay and a controller I believe as well . Can we start with the last 8 digits of the vin number please . I will look up the diagram for your specific truck and send it to you so we can diagnose this further .

Customer: replied 1 year ago.
The last 8 of the vin is WH547460 The relay has been replaced between the master cyl and the hydroboost. The master cyl, hydroboost, sensor on master cyl, and sensor on hydroboost, the power steering pump, motor on the hydroboost, have all been replaced and it still continues to run the hydroboost motor continuously unless you unplug it from the master cylinder. I don't know what else to do. Do you think it could be the pressure differential valve stuck in the master cylinder even though it is new?
Before I replaced all of these parts, it was hard to steer and everytime you moved the steering wheel, the brake pressure light would come on and so would the hydroboost motor.....and if I hold pressure on the brake then the light would come on the brake pressure light and the hydroboost motor would come on also. But now that I have replaced all these parts, the power steering works fine, but the brake presssure light stays on continuously, and the hydro boost motor still runs constantly.
Everybody I have asked says they have no clue on what to do next. Please help!
Expert:  Andy replied 1 year ago.

Here is the wiring diagram :

Expert:  Andy replied 1 year ago.

If you unplug the relay , does the brake motor continue to run ?

Customer: replied 1 year ago.
Hello, I have answered this but it keeps telling me to click on the button above to answer and there is no button to click on..... this is becoming soooo frustrating.NO, it cuts off if you unplug the relay. We have bled the brakes over and over and that hasn't helped either. We have replaced the master cylinder and the sensor on it...... replaced the flow switch, new hydro boost and hydro boost motor and power steering pump. Still the hydro boost motor continues to run and the brake pressure light continues to stay on. With the ignition off and you hit the brake the hydro boost motor comes on and if ya let off of the brake the hydro boost motor cuts off.
If you cut the ignition switch on it constantly runs without hitting the brake and if you start it up, it constantly runs without hitting the brake.
Expert:  Andy replied 1 year ago.

Ok thanks for the info . Reconnnect all , then disconnect the flow switch while engine is running . What happens to the brake motor ?

Expert:  Andy replied 1 year ago.

Have you tried what I suggested last ? What was the outcome?

Customer: replied 1 year ago.
We tried that and it kept running. Come to find out the valve kept sticking in the brand new master cylinder causing the sensor to be pushed in.....
Expert:  Andy replied 1 year ago.

Ok so my diagram helped you! Let me know if you need help with anything else! Please do not forget to rate my service . Feedback is important . Thanks