OE end plugs are designed to prevent critical pressure loss by capping the bore, while also functioning as a valve stop. Repetitive spring motion, valve impact and fluid pressure variations cause wear between the end plug and bore mating surface, allowing vital pressure to escape the circuit. GM 4L80-E and 4L85-E pumps have end plugs at the pressure regulator and TCC shift valves that seal signal oil required to stroke the valve. When excess wear occurs at the end plugs, the result can be shifting problems, loss of gear and/or converter-related concerns.
Stop leaks and revive line pressure and TCC operation by installing Sonnax O-ringed end plug kit 34200-05K.