GM Service Manual Online
For 1990-2009 cars only
  1. Apply the parking brake.
  2. Drain all of the reservoirs. Refer to Draining Reservoirs .
  3. Start the engine and run the engine at a fast idle.
  4. Verify that the low pressure tone alarm is on.
  5. •  If the tone alarm is not on when first charging the system, test the brake warning system.
    •  For diagnosis of the brake warning system, refer to Brake Warning Alarm Inoperative.
  6. The low pressure tone alarm should turn off when the dual air pressure gauge indicates 470-510 kPa (68-74 psi).
  7. •  If the tone alarm does not turn off, test the brake warning system.
    •  For diagnosis of the brake warning system, refer to Brake Warning Alarm Always On.