Transmission Diagnostics

A failed low roller one-way sprag in a 4L60E — a mechanical failure that causes loss of first gear or starting in second. If a 4L60E won’t shift out of 1st gear, the most common causes are: Low line pressure Worn valve body Accumulator issues Failed low roller sprag Internal clutch damage After rebuilding these units for over 40 years, I can tell you this: when a 4L60E hangs in 1st, you need to stop guessing and start checking the system the right way. Common symptoms If you’