Combination (Proportioning) Valve

Pressure Differential Switch
1. Have helper sit in drivers seat to apply brake pedal and observe red brake warning light.
2. Raise vehicle on hoist.
3. Connect bleed hose to a rear wheel cylinder and immerse hose end in container partially filled with brake fluid.
4. Have helper press and hold brake pedal to floor and observe warning light.
a If warning light illuminates, switch is operating correctly.
b If light fails to illuminate, check circuit fuse, bulb, and wiring. The parking brake switch can be used to aid in identifying whether or not the brake light bulb and fuse is functional. Repair or replace parts as necessary and test differential pressure switch operation again.
5. If warning light still does not illuminate, switch is faulty. Replace combination valve assembly, bleed brake system and verify proper switch and valve operation.