GM Service Manual Online
For 1990-2009 cars only
  1. Block the wheels.
  2. Start the engine.
  3. Charge the system air pressure to the governor cut-out point.

  4. Object Number: 209561  Size: SH
  5. Pull out the trailer air supply knob (3).

  6. Object Number: 209563  Size: SH
  7. Pull out the system park knob (1).

  8. Object Number: 209561  Size: SH
  9. Apply a soap solution to the exhaust vent and around the base of the trailer air supply knob (3).
  10. Verify that leakage is less than a 25 mm (1 in) bubble in 5 seconds. If not, replace the valve. Refer to Trailer Brake Supply Valve Replacement or overhaul the valve. Refer to Air Brake System Description and Operation .
  11. If the leakage exceeds these limitations, replace the valve. Refer to Trailer Brake Supply Valve Replacement or overhaul the valve. Refer to Air Brake System Description and Operation .
  12. Push in the trailer air supply knob (3).

  13. Object Number: 209563  Size: SH
  14. Apply a soap solution to the exhaust port.
  15. Check that the leakage is less than a 25 mm (1 in) bubble in 5 seconds.
  16. If the leakage exceeds these limitations, replace the valve. Refer to Trailer Brake Supply Valve Replacement or overhaul the valve. Refer to Air Brake System Description and Operation .
  17. Set the parking brake.
  18. Remove the wheel blocks.