wont go into 1st, even though PCM is commanding Please help

mz0dw4 · February 28, 2017

1995 Chevrolet Silverado 2WD, 5.7 Litre, OBD1 with rebuilt 4L60E – worked for about a week, then went into fail safe mode. Here are the symptoms: From Drive or O/D, won't start in 1st or 2nd gear – stuck in 3rd, feels like the brakes are applied. The only way to get it to start moving from a dead stop is to manually downshift to 1st or 2nd which is always 2nd gear. After manually shifting to 1st or 2nd, it starts moving but the vehicle is really in 2nd gear. (will not drop to 1st at all – No matter what.) Once you manually downshift to either 1st or 2nd, it will take off in 2nd gear. Then if you manually shift to OD, it shifts through the rest of the gears fine including TC lockup. Once on the highway cruising speed, it will downshift to 3rd and back to 4th, and lockup OK. Once you slow down to a stop, the process needs repeated to get back up to speed ,like driving a manual shift without 1st gear! I have tested ALL solenoids, wiring, fuses, PCM, etc. A tech hooked a Snapon Versa scanner which says no engine codes or transmission codes are throwing. The tech said that per the scanner, all input sensors to the PCM which control the trans are operating OK and the trans showed all gears as correct. Tech insists, and I watched as we drove around that the PCM is commanding the solenoids but still wont go into 1st. I'm at my wits end and need an expert. Could the 1-2 shift valve be stuck, or the spring broke. What would make the trans not go into 1st other than an internal trans issue. Please help if you can. I have many more details once the conversation starts.

gmguy1982 · March 6, 2017

It does sound like maybe the 1-2 downshift spring is broke. This problem happens a lot from what i saw when i remanufactured 4l60e valve bodies. easiest thing you could do is replace the valve body. I did a v.b. swap in my silverado and it fixed my p1870 code. global transmission parts.com is where i got the valve body ready to install.

mz0dw4 · March 7, 2017

OK guys, after pulling the pan here is what I found. Nothing alarming in the pan as far as shavings,etc. I unplugged both solenoid A and B and probed the connectors with the key on and both had 11.94 volts. So, I got 2 brand new solenoids, tested them and they ohmed out OK. Now, here is the weird part. I plugged in Solenoid A and B and turned the key on and probed the back side of the connector, it did not show 12v, to my surprise it shows 0.0 volts. That doesn't sound normal, I was expecting 12v since in park they should both be energized. I think my ignition switch may be bad and it can carry the 12v, but not the amps required to energize the solenoids. Let me know what your thoughts are on this. I think I've found an issue.

ifixedit · March 16, 2017

Check out this thread here, might be worth looking into for you as well as the symptoms are very similar >>> http://www.gm-trucks.com/forums/topic/198936-transmission-problems/