I dont consider myself an expert on the 4L60E boxes,I have changed a few but never really got into the internals much. I believe there are 8 or 9 selenoids in your trans and one of them controls converter lock up.I believe the PCM gets its signal from the speed sensor and the PCM signals one of the trans selenoids to lock up the converter. Their are many people on this site that have a ton more knowledge that I on this trans,but I would think its either a bad selenoid or speed sensor. Before doing anything I would crawl under your machine and check to see that all the
wiring to your trans is plugged in properly. Also check to see that no wires are pinched in between the trans and engine . What does the shop say about your trans, they should have some input. good luck. ed
wiring to your trans is plugged in properly. Also check to see that no wires are pinched in between the trans and engine . What does the shop say about your trans, they should have some input. good luck. ed