August 21, 2013
Vehicles with GM 6L45, 6L50, 6L80 and 6L90 transmissions may have a number of TCC apply problems. Bore wear at the TCC regulator valve can cause no TCC apply or slipping on engagement, harsh shifts, loss of performance and fuel economy and fluid overheat. If the valve is stuck in the apply position, the result is harsh TCC apply. If the valve is stuck in the release position, no TCC apply or TCC slip will result.
For moderately worn bores, installing Sonnax TCC regulator valve kit 104740-46K will restore proper valve function resulting in proper TCC apply. The valve lands have been lengthened significantly, allowing the valves to operate in unworn portions of the casting bore to effectively seal against leakage.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.