For 1990-2009 cars

Problem | Action
--- | ---
The air brake dryer desiccant cartridge requires replacement. | Replace the desiccant cartridge.
The air system was charged from an external air source. Air is not passing through the air brake dryer. | Decrease use of the inflation valve in order to charge the system.
The air brake dryer is not purging. | Refer to Desiccant Being Expelled From Purge Valve Exhaust .
The purge (air exhaust) time is too short because of excessive system leakage. | Refer to Desiccant Being Expelled From Purge Valve Exhaust .