- Block the wheels.
 
- Start the engine.
 
- Charge the system to the air compressor governor cut-out point.
 
- Stop the engine.
 
- Push down the trailer air brake control
valve
lever to the full off position.
 
- Inspect the valve body and the exhaust port for any air leakage.
 
If any air leakage is present, replace the trailer air brake control
valve.
- Pull up the trailer air brake control lever to the full on position.
 
- Inspect the valve body and the exhaust port for any air leakage.
 
If any air leakage is present, replace the trailer air brake control
valve.
- Remove the wheel blocks.