In a 1999 Chevy Astro van what is the most common reason for 4 wheel drive light to come on?

In a 1999 Chevy Astro van, the most common reason for the 4-wheel-drive light to come on is a problem with the shift motor or actuator. This is often due to a faulty motor itself, a wiring issue, or low fluid level in the transfer case. Other possibilities include issues with the transfer case itself, but the shift motor is usually the culprit.