GM Service Manual Online
For 1990-2009 cars only
  1. Coat the safety valve exhaust vent with a soap solution.

  2. Object Number: 202784  Size: SH
  3. Check that the leakage is less than a 25 mm (1 in) bubble in 5 seconds.
  4. Replace or overhaul the valve (1) if leakage exceeds these specifications. Refer to Primary Air Brake Supply Reservoir Safety Valve Replacement or Air Brake System Description and Operation .