The oil level is low.

Add oil in order to acquire the proper oil level. Refer to Transmission Fluid Check .

The external filter is clogged.

Replace the external filter. Refer to External Transmission Oil Filter Replacement .

The seal ring on the intake tube is leaking or missing.

Install a new seal ring onto the top end of the intake tube.

The main pressure regulator valve spring is weak.

Replace the spring.

The control valve body is leaking.

Replace or rebuild the valve body assembly.

The valves of the trimmer relays and main pressure regulator are sticking.

Replace or rebuild the valve body assembly.

The input charging pump is worn or damaged.

Replace or rebuild the pump.

The priority valve is missing.

Replace the missing valve.