Toyota Repair: 4 wheel drive instument panel light display, vacuum lines, drive lever

Question
I drive my 98 4 Runner, auto trans, once a week.It has about 40,000 miles and is in excellent condition. Today, during my weekly drive to the gym, I shifted the 4 wheel drive lever into high 4 from high 2. Normally a lighted illustration appears on the dash but it would not come on today no matter what I did. Also, it definitely did NOT feel that it was in high 4. When I shifted to Low Low, it engaged but still no display. Any suggestions please? Thanks and have a good thanksgiving!
Scott

Answer
Unless the indicator light on the dash is on it is not in 4x4, the front axle uses the (ADD) automatic differential disconnect) system, it has an actuator mounted on the front differential which locks the front diff to the axles to provide front wheel drive.
There are a couple of reasons this may not be happening, there may be a leak in one of the vacuum lines to the actuator, the metal pipes to the actuator may be clogged with rust or one of the vacuum switching valves is malfunctioning or the actuator has an internal leak.