STL010 Transmission Cooler Bypass Upgrade Kit GM 6L80 6L90 8L90 10L90 15251488
The factory-installed thermal bypass valve (TBV) on GM 6L80, 6L90, 8L90, and 10L90 automatic transmissions is a notorious point of failure. The internal wax pellet often sticks in the closed position, blocking transmission oil from flowing to the external cooler.