If there is a pressure loss greater than 80 psi on on side of the system, the driver will be alerted because the brake differential pressure switch is wired to the warning light in the dash. This switch does not control the pressure flow on either side of the vehicle, but it can prevent fluid flow if it has to. A light on the dashboard will come on if the pressure switch is defective.
If a warning light in your vehicle indicates that the pressure switch is defective than inspect the electrical connections going from the switch to the brake light. Inspect for loose connections and if there are any, tighten them with a wrench. If all the connections are tight, then shut off the car’s engine and pop the hood.
Look for the brake differential switch, which is generally located between the front and rear brakes, near the master cylinder. Gently pat around the switch with your fingers to see if there is moisture, which usually means leaking brake fluid. You will need to replace the O rings if this is the case, which helps create a tight seal so there is no leaking.
Pop off the old O-rings with a flat head screwdriver blade. These shouldn’t come off with much difficultly.
Add a light layer of engine lubricant to the base of the new O-ring. Push the new O-ring into place on the tip of the switch. Gently shove the O-rings all the way to the end until they are plumb against the master cylinder. If there are still leaks, you may need to replace the brake differential pressure switch altogether. Unless you have extensive mechanical knowledge, you shouldn’t replace the switch by yourself.
Necessary Materials
Flathead screwdriver
O-rings for a brake differential switch
Engine lubricant