GM Service Manual Online
For 1990-2009 cars only

Important: Review the system description and operation in order to familiarize yourself with the system functions. Refer to the following:

   •  Brake Warning System Description and Operation
   •  Air Brake System Description and Operation
   •  Air Drum Brakes Description and Operation
   •  Disc Brake System Description and Operation

Visual/Physical Inspection

    • Inspect for aftermarket devices which could affect the operation of the hydraulic brake system. Refer to Checking Aftermarket Accessories .
    • Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
    • Inspect the brake fluid reservoir for the proper brake fluid level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:

    •  Low Air Indicator Always On
    •  Low Air Indicator Inoperative
    •  Air Brakes Application Slow
    •  Air Brake Safety Valve Deploys
    •  Braking Action Uneven - Front to Rear
    •  Braking Action Uneven - Side to Side
    •  Air Brakes Drag
    •  Air Brake Dryer Constantly Cycling or Purging
    •  Air Brake Dryer Safety Valve Exhausting Air
    •  Air Brake Dryer Purge Valve Exhausting Air
    •  Air Brake Dryer Does Not Purge or Exhaust Air
    •  Desiccant Being Expelled From Purge Valve Exhaust