For 1990-2009 cars

1. Apply the vehicle parking brake.
2. Drain all the reservoirs. Refer to Draining Reservoirs .
3. Start the engine and charge the air system to the governor cut-out point.
4. Verify that a discharge of air occurs at the air brake dryer exhaust port. This is the air brake dryer purge cycle. If the air brake does not cycle properly, check for air leaks in the air brake dryer system. Refer to Automatic Level Control Air Dryer Replacement . If needed, replace the air brake dryer.