For 1990-2009 cars

1. Apply the parking brake.
2. Block the wheels.
3. Start the engine. Charge the air system to the maximum pressure limit of 860 kPa (125 psi).
4. Place the differential lock control valve in the ON position.
5. Stop the engine.
6. Coat all of the air line connections with a soap solution in order to inspect for leaks. Air leakage is not allowed. If any leaks are present, repair the leaks as needed. Refer to Air Brake Dryer Testing .
7. Coat the entire surface of the driver controlled differential lock shift cylinder using soap suds in order to inspect for leaks. If any leaks are present, repair or replace the driver controlled differential lock shift cylinder.
8. Remove the wheel blocks.