My check engine light is on, when they use machine to scan clear it, it comes immediately I moved the car. Any cause of problem and solution? Thanks

Check engine ,4x4 air bag etc is always on
The 4x4 is not functioning anymore.

After scanned using OBDII reader engine light off and all test passed. And it appear on again few days.

Check engine light on after scan showing code p0451

Showing check engine light

The check engine light is showing