Here is what is in the service manual
AUTO Mode
Vehicle will switch automatically to AUTO mode if vehicle speed increases. If vehicle speed then decreases, the vehicle automatically returns to direct 4-wheel driving conditions.The AWD LOCK indicator lamp keeps illuminating.
LOCK mode will change to AUTO mode automatically, when the vehicle speed exceeds approx. 10 km/h (6 MPH) for a long time. The AWD LOCK indicator lamp turns off.
When the vehicle speed exceeds approx. 10 km/h (6 MPH), AUTO mode cannot be shifted to LOCK mode. In contrast, LOCK mode can be shifted to AUTO mode.
LOCK mode will change to AUTO mode automatically, when the ignition switch is turned “OFF”.
NOTE:
Every time AWD LOCK switch is pressed, AUTO mode and LOCK mode switch each other.
When driving in AUTO mode or LOCK mode, if there is a large difference between front and rear wheel speed which continues for a long time, oil temperature of drive system parts becomes too high and AWD warning lamp flashes rapidly. (When AWD warning lamp flashes, vehicle changes to front-wheel drive
conditions.)
If AWD warning lamp is flashing rapidly, stop vehicle and allow it to idle for some time. Flashing will stop and AUTO mode will be restored.
When driving in AUTO mode, AWD warning lamp may flash slowly if there is a significant difference in diameter of the tires. At this time, vehicle performance is not fully available and cautious driving is required. (Continues until engine is turned OFF.)
If the warning lamp flashes slowly during driving but remains OFF after engine is restarted, the system is normal. If it again flashes slowly after driving for some time, vehicle must be inspected.
If there is a difference of revolution speed between the front and rear wheel with AUTO mode the shift occasionally changes to LOCK mode automatically. This is not malfunction.
If there is a significant difference in pressure or wear between tires, full vehicle performance is not available. Tire conditions are detected, and LOCK mode may be prohibited, or else speeds at which LOCK mode is enabled may be restricted.
AWD LOCK INDICATOR LAMP
The following is the indications of indicator lamp.
AWD WARNING LAMP Turns ON when there is a malfunction in AWD system. It indicates that fail-safe mode is engaged and vehicle change to front-wheel drive or shifting driving force-AWD (Rear-wheels still have some driving torque). Also turns ON when ignition switch is turned ON, for purpose of lamp check. Turns OFF approximately in 1 seconds after the engine starts if system is normal.
Condition AWD LOCK indicator lamp
AUTO mode OFF
LOCK mode ON
Lamp check Turns ON for approx. 1 second when ignition switch is turned ON.