Vehicles with listed Toyota/Lexus transmissions may exhibit insufficient line rise in drive ranges 4th-6th Gears causing shift complaints and burnt C4 clutches. These problems may be caused by continuous oscillation of the C4 apply boost valve within the sleeve, creating excessive wear and a path for line pressure fluid to leak to exhaust. Sonnax C4 apply boost valve kit 168740-02K has upgraded materials and minimal clearances to prevent wear and restore proper hydraulic control.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.