Vehicle Tow Protection Valve Operational Check Operational Check

1. Block the wheels.
2. Start the engine.
3. Charge the system to the air compressor governor cut-out point.
4. Stop the engine.
5. Connect an air pressure test gauge to the trailer air supply service coupling.
6. Pull up the trailer air brake control lever to the fully applied position.
7. Verify that pressure occurs at the trailer service air line coupling.
8. Push down the trailer air brake control lever to the full released position.
9. Ask an assistant to apply the brake pedal firmly.
10. Inspect for air leakage at the exhaust port of the trailer air brake control valve. Excessive leakage indicates a faulty double check valve shuttle within the towing vehicle protection valve.

If the leakage is excessive, overhaul or replace the towing vehicle protection valve.

11. Release the brake pedal.
12. Disconnect the air pressure test gauge from the trailer air supply service coupling.
13. Start the engine.
14. Charge the system to the air compressor governor cut-out point.
15. Stop the engine.
16. Check the brakes for proper operation.
17. Remove the wheel blocks.

Vehicle Tow Protection Valve Operational Check Leakage Test

1. Block the wheels
2. Start the engine.
3. Charge the system to the air compressor governor cut-out point.
4. Stop the engine.
5. Pull out the trailer air supply knob.
6. Disconnect the trailer air service air line.
7. Pull up the trailer air brake control valve lever in order to fully apply the trailer service brakes.



8. Hold a finger over the 1.6 mm (0.0625 in) vent hole in the valve.
9. Inspect the hose coupling and the exhaust port for leakage. If the air leakage is excessive, overhaul or replace the towing vehicle protection valve.
10. Release the trailer air brake hand control valve.
11. Connect an air pressure test gauge to the trailer air supply service coupling.
12. Pull up the trailer air brake control lever to the fully applied position.
13. Inspect for air leakage at the exhaust port. If the air leakage is excessive, overhaul or replace the towing vehicle protection valve.
14. Inspect the 1.6 mm (0.0625 in) vent hole in the valve for air leakage. Leakage is not permissible.

If the air leakage is present, overhaul or replace the towing vehicle protection valve.

15. Push down the trailer air brake control lever.
16. Inspect the 1.6 mm (0.0625 in) vent hole in the valve for air leakage. Leakage is not permissible.

If the air leakage is present, overhaul or replace the towing vehicle protection valve.

17. Drain all of the air from all of the lines and the air reservoirs.
18. Disconnect the air pressure test gauge from the trailer air supply service coupling.
19. Start the engine.
20. Charge the system to the air compressor governor cut-out point.
21. Stop the engine.
22. Check the brakes for proper operation.
23. Remove the wheel blocks.