4L60E Shift Problems?

Lodogg2221 · November 2, 2005

1998 Chevrolet K1500 Z71, 5.7, 137,000 mi, Short bed, Ex cab. K&N FIPK, Flowmaster cat back, Flex-a-lite fans.

OK, About a year and a half ago, I had the solenoid/valve sleeved (1870 code) and replaced....solved my hard 1-2 shifting problem. No problems till now. The other day, while driving on the highway, my check engine light came on, no noticable problems, but I stopped at Autozone to get the codes read, but the guy erased them before he told me what they were! Anyway, I bought a new batttery at the time because earlier in the day the voltage dropped pretty low while the truck was running (VERY old battery, needed it for a while), but this was a first for as low as it got! After was when I noticed the light. ANyway, fast forward to today, 3 days later. I started my truck after having it sit for a few hours, and when I shifted into drive it was a very solid engagement. A LOT more than normal. As I pulled off, it shifted into 2nd very hard as well, just like it did when I had to have the valve fixed. After than though, it would not return to 1st gear. I drove home, thru town, so not over 30mph, parked it. Went out a few minutes later so I could take it to the shop who originally fixed it, and it ran just like it was supposed to.

The codes he pulled are: 720 - Output Speed Sensor Malfunction

785- Shift/Timing Solenoid Malfunction

1860- TCC PWM Solenoid Circuit Electrical

He says he doesnt have a clue what it could be since he couldnt reproduce it, but Im worried because of the damage it may cause. Pretty sure the valve is fine, but surely this isnt a first......

GM-Tech · November 2, 2005

The 785 and 1860 are electrical problems. As for the 720, I find no such code listed for a 1998 truck in any area.

If all the codes occur at the same moment, I would suspect wiring. It's highly unlikely a couple different solenoids would intermittently have a problem at the exact same moment.