February 21, 2013
GM 4L80-E and 4L85-E transmissions may have 2nd gear starts and no upshifts, which can be accompanied by trouble codes 68, 85, 86 and/or 87. These problems can often be traced to a leaking actuator feed limit (AFL) filter or end plug. Installing Sonnax AFL filter end plug and O-ring kit 34994-17K eliminates these problems by restoring hydraulic control to the circuit.
For a more comprehensive AFL circuit repair, recommend also installing Sonnax actuator feed limit valve kit 34200-16K.