1997 3500 4l80e problems

[Truckracer]

Truck has always been perfect until a week ago. Took off for town and the trans was in second gear and then started shifting between second and first, rapidly. I slowed down some and then it just went to second and stayed, limp mode I assume. no check engine light, no codes with my scanner (which I'm not sure can see transmission codes). Did a little research and talked with a transmission guy. So, at this point I've changed the fluid and filter, both shift solenoid's, TPS, and both speed sensors.
It's no longer in limp mode - it just starts out in second, then shifts erratically back to first or to third no matter the speed or throttle input.. I'm about ready to burn it down...


Truck has 121,000 miles on it. Fluid and filter looked great - nothing in the pan at all.

 

[Dropped88]

Check the electrical connector on side of trans for fluid in the connector. Common problem and causes really weird issues. And need to verify that you can read trans codes. If not you could be chasing your tail

 

[leakers]

Stuck in second means both solenoids are off..i.e. no power to either of them. If cleaning the connectors , ( use a high quality electronic spray and compressed air, and then diaelectric grease in the connector once you know it is working again. ) It does help to visually check the pins and the wiring itself. loose pins (not good enough connection) is also a problem. It is quite common for the loom to get damaged up near the firewall on top of the trans . or wires to get broken in the loom. Sometimes if they have had oil on the loom the insulation will break down and cause shorts between the different wires .

Shift Solenoid Pattern​

	1-2 Solenoid	2-3 Solenoid
1st Gear	On	Off
2nd Gear	Off	Off
3rd Gear	Off	On
4th Gear	On	On

No power results in 2nd Gear as 'Limp home mode'.

 

[Supercharged111]

My harness on my 1500 leaked after reassembly so I bought a new one. My dad had a harness go bad and left him in limp mode. I potted the back side of the new harness with grey silicone.

 

[stutaeng]

Looks like page 44 of this source may be your problem:

https://www.google.com/url?sa=t&source=web&rct=j&url=https://gear-report.com/wp-content/uploads/2017/03/Supplement_7_4L80E-Transmission_Troubleshooting.pdf&ved=2ahUKEwiO7oXeqMLyAhWqVzABHW9-A0EQFnoECA4QAQ&usg=AOvVaw0kjoWGa02i3OULRIwx35i0