The differential lock system is an electric/air operated system with an electrical circuit used to control the air supply with a differential lock control valve and a differential lock indicator. The electrical diagnostics will only diagnose the electrical portion of the system and assumes the air operated portion is operating normally. Voltage is supplied from the #9 circuit breaker through the ignition 3 voltage circuit to the differential lock switch. When the differential lock switch is pressed the contacts internal to the switch close. With the differential lock switch closed voltage is supplied to the differential lock indicator, illuminating it, and ground is provided by splice pack 2. Voltage is also supplied to the differential lock control valve activating the solenoid to supply the system with air pressure. Ground is supplied by G107. The air pressure is used to engage a piston in the power divider mounted to the differential carrier assembly. This locks the left and right side axle shafts so no differential action takes place and torque is transmitted equally to both wheels.

When the differential lock switch is pressed again, the switch contacts open removing voltage from the differential lock indicator and the differential lock control valve. Air pressure is released from the system allowing a compression spring to return the piston disengaging the differential lock.

View the list of major components that make up the electric/air operated differential lock system below.

The differential lock switch is mounted to the dash panel.

When the differential lock switch is pushed to the ON position, the differential lock is engaged. This condition allows torque to be transmitted equally to both axles without differential action.

When the differential lock is pushed to the OFF position, the differential lock is disengaged. This condition allows torque to be transmitted to both axles through differential action.

The differential lock control valve is an electrically actuated solenoid type valve. The control valve is located on the crossmember forward of the rear axle front unit. It supplies air pressure to the system in order to engage the differential lock.

The differential lock pressure protection valve is a normally closed pressure sensitive type control valve. It protects the vehicle's air system if a failure occurs in the differential lock air system.

The air cylinder/differential lock assembly is part of the power divider, which is mounted to the differential carrier assembly. When air is supplied to the air cylinder/differential lockout, the shift fork shifts the lockout sliding clutch and engages the differential lock. When the air supply is removed, the compression spring disengages the differential lock.