4WD vehicles can be shifted electronically or manually. Electronic 4WD vehicles have warning lights to inform the driver if there’s a problem with the system. Different manufacturers use different transfer cases and control systems on their part time 4WD vehicles. Typically the indicator light flashes while the vehicle is shifting. Once the vehicle is in the desired mode the light should remain solid indicating that the shift into that mode is complete. There’s a problem if the light continues to flash or flashes for a while and then goes out without completing the shift.
This problem is typically caused by wiring or an electrical component like the controller, a faulty motor, speed sensor or position switch. Many 4WD units have an actuator located on the front axle to lock and engage the front axle for 4WD. If this actuator or its shift fork is faulty, the vehicle will remain in 2WD and the light will flash indicating a problem to the driver.
Check to see if the vehicle is in 4WD; typically, if the vehicle does not have a locking differential and did not complete its shift into 4WD the front tire should spin easily. Jack up the one side of the front of the vehicle and spin the tire. If the tire spins freely the vehicle is in 2WD, if the tire is hard to turn or is locked, it’s in 4WD. Be careful though, a 4WD vehicle that does not contain a center differential can wind up if driven on dry pavement. This will cause the front tire to spin with great force when the front tire is jacked off the ground. This is known as drivetrain windup.