If you have this light, it should come on briefly when you turn on the ignition, as a check to show you it is working.

The SERVICE 4WD light comes on to indicate that there may be a problem with the four-wheel drive system and service is required. Malfunctions can be indicated by the system before any problem is apparent, which may prevent serious damage to the vehicle. This system is also designed to assist your service technician in correctly diagnosing a malfunction.