GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Air Brakes 🢒 Vehicle Tow Protection Valve Operational Check
  1. Block the wheels.
  2. Start the engine.
  3. Charge the system air pressure to the governor cut-out point.
  4. Pull the tractor park knob if present out.
  5. Disconnect the trailer service line hose coupling.
  6. Move the trailer brake control valve lever in order to fully apply the trailer service brakes.
  7. Hold a finger over the 1.6 mm (1/16 in) vent hole in the valve.
  8. Check for leakage at the hose coupling and the exhaust port.
  9. If leakage is excessive, replace or overhaul the valve. Refer to Towing Vehicle Protection Valve Replacement or Air Brake System Description and Operation .
  10. Apply the trailer brake control valve lever.
  11. Turn the ignition ON and check for stoplamp operation.
  12. Release the trailer brake control valve lever.
  13. Check if there is pressure at the trailer service hose coupling.
  14. Check for leakage at the exhaust port.
  15. If leakage is excessive, replace or overhaul the valve. Refer to Towing Vehicle Protection Valve Replacement or Air Brake System Description and Operation .
  16. Release the trailer brake control valve lever.
  17. Firmly apply the brake pedal.
  18. Check for leakage at the trailer air brake valve exhaust port.
  19. If leakage is excessive, replace or overhaul the valve. Refer to Towing Vehicle Protection Valve Replacement or Air Brake System Description and Operation .
  20. Release the brake pedal.
  21. Drain all of the air from all of the lines and the reservoirs.
  22. Disconnect the air pressure test gage and the service hose coupling.
  23. Set the parking brakes.
  24. Remove the wheel blocks.