In GM 4T40-E and 4T45-E units, the boost valve assembly is activated by torque signal pressure from the pressure control solenoid and reverse pressure to aid in adjusting line pressure at the pressure regulator valve. This boost valve is continuously oscillating in the sleeve, which leads to wear and hydraulic leakage. When wear occurs, critical oil pressure is allowed to cross leak between the circuits or leak to exhaust. These leaks can result in either no line rise or an unwanted increase in line pressure. Sonnax boost valve kit 33886-03K that the hydraulic integrity and controls line rise.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.