For 1990-2009 cars

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 in Air Drum Brakes

• | Disc Brake System Description and Operation in Disc Brakes

### Visual/Physical Inspection

• | Inspect for aftermarket devices which could affect the operation of the Hydraulic Brake System. Refer to Checking Aftermarket Accessories in Wiring Systems.

• | 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 in Wiring Systems.

### Symptom List

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

• | Brake Warning Alarm Always On

• | Brake Warning Alarm Inoperative

• | 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 Make Grinding Sound When Applied

• | Air Brakes Drag

• | Air Brake Dryer Constantly Cycling or Purging

• | Air Brake Reservoirs Contain Water

• | 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

• | Air Dryer and/or Moisture Ejector Inoperative