GM Service Manual Online
For 1990-2009 cars
Makes 🢒 Chevrolet 🢒 2004 🢒 C-Series Medium Duty Truck C6/7/8 - Mexico 🢒 Brakes 🢒 Air Brakes 🢒 Trailer Brake Control Valve Operational Check
  1. Block the wheels.
  2. Test the vehicle dual air pressure gage with the test gage.
  3. Install the test air pressure gage in the valve delivery line.
  4. Start the engine.
  5. Charge the system air pressure to the governor cut-out point.

    6. Object Number: 202866 Size: SH
  6. Move the trailer brake control valve lever (1) counterclockwise to the full OFF position.

    7. Object Number: 202795 Size: MH
  7. Check that the test air pressure gage indicates zero air pressure.
  8. Replace or overhaul the control valve (5) if the air pressure does not indicate zero. Refer to Trailer Brake Control Valve Replacement or Air Brake System Description and Operation .

    9. Object Number: 202866 Size: SH
  9. Move the trailer brake control valve lever (1) clockwise to the full ON position.

    10. Object Number: 202795 Size: MH
  10. Check that the test air pressure gage indicates the same air pressure as the dual air pressure gage.
    11. • If the pressure is not the same, adjust the valve (5). Refer to Air Compressor Governor Valve Adjustment in Air Compressor.
    •  If the valve (5) does not deliver full pressure after the adjustment, replace or overhaul the valve (5). Refer to Trailer Brake Control Valve Replacement or Air Brake System Description and Operation .

    Object Number: 202866 Size: SH
  11. Move the trailer brake control valve lever (1) to several intermediate positions.
  12. Drain the air system reservoirs. Refer to Draining Reservoirs .
  13. Remove the test air pressure gage.
  14. Check the operation of the brakes.
  15. Remove the wheel blocks.