The operating pressure is too low.

(1) The amount of oil in the gearbox oil pan is insufficient;

(2) Oil leakage in the main oil pipe;

(3) The gearbox filter is blocked;

(4) The steering pump (or hydraulic pump) is damaged, causing serious internal leakage;

(5) Improper pressure adjustment of transmission pressure regulating valve;

(6) The gear-shifting pressure valve spring fails or breaks.