Transmission 4L80E not shifting out of 2nd gear

[chris_maxwell]

Put new tires on my truck and going home I decided to give it a little tune-up (blow some smoke out). So at a stop light I put it in 1st gear and it jumped to 2nd before I move the shifter. Next after I let off of the throttle the tranny was slipping. It did this, I was only able to go about 30mph until I came to a place I could pull over. Fluid level was good, but color might be a little dark. I restarted the truck and it ran fine until I tried to manually shift again and it repeated itself to not shift into 3rd gear. Shut down and restart, runs and shifts but not sure it is normal. I checked codes and got DTC 39(TCC Stuck Off), DTC 68 (Transmission component slipping), and DTC83 (TCC PWM Solenoid Circuit Fault). Any ideas on what’s happening? I have 127,000 miles on it, a 1995 4 X 4.

[Robyn]

Check all the grounds in the tranny circuit.

You may have a solenoid thats not working right under manual conditions.

These little beasts have a switch on the outside of the shift shaft that tells the puter what gear is selected. If this switch is having issues it can cause the puter to screw things up and result in the codes.
The solenoids could be getting issues too.
There is also a set of pressure switches inside too.
Lots of stuff happening in these trannies to make it all work.

Check the connections, grounds and such and then its off to the rodeo to figure out whats going on.
You really could use a tech tool to check and see if the selected range is what the computer is seeing when things are running.
As longs as its working fine in the D range I would not suspect anything major as far as components go.

Run it normally and dont continue to cause it to slip.

Good luck

Robyn

[chris_maxwell]

Where will I find all of the tranny grounds? I tried to take it to a shop today but they were closed. I was going to have them change the fluid and filter and take a peek at everything.

[Cowracer]

also check your input and output shaft speed sensors.

If one of those fail, or gets flaky, the computer will command a 'limp' mode. I belive limp mode engages second only.

If your speedo dies during this, I'd strongly suspect the output shaft speed sensor. if the speedo is normal, look at the input shaft one.

Tim

[donbfishin]

My 4L80 is doing the same thing, have a appointment for Wednesday to replace both speed sensors. In regards to Robyn's statement about a switch to tell the computer what gear you select, where is it & does anyone have a part number ? My parts buddy can't find it listed...

Don

95 K2500, 6.5 TD, Sol D, 4L80, 3.73, Kennedy chip & exhaust, gauges, Auburn posi, Bilstiens, added grounds, 2/0 gauge battery cables, much more.

[donbfishin]

No replies ?? Where is the shift switch as previously asked ?
Don
Sig. above

[93_Burrito]

'95 model year trucks seem especially prone to transmission issues due to a faulty/failing ignition switch. A bad ignition switch will put the transmission in limp mode (2nd gear only).

Ever notice the transmission gear selecter light on the dash blinking on or off intermittently?


Andy

[donbfishin]

I did see the indicator lite blinking one time. There is a updated front sensor, so didn't get it replaced today, but bakelite is cracked around center metal contact. Have tried key no / off several times, no change in shifting pattern.
Don

[chris_maxwell]

I changed the filter, fluid, and added a quart of Lucas (don't know if this was a good idea) but it doesn't seem like it has the pull out of 1st gear, and if i manually try to shift it jumps itself out of 1st into second early. Is there a place to find these sensors? I didn't find any metal in my tranny pan but the fluid was brownish. In the 99 upgrades what all was changed?

[Cowracer]

I changed the filter, fluid, and added a quart of Lucas (don't know if this was a good idea) but it doesn't seem like it has the pull out of 1st gear, and if i manually try to shift it jumps itself out of 1st into second early. Is there a place to find these sensors? I didn't find any metal in my tranny pan but the fluid was brownish. In the 99 upgrades what all was changed?

on a 2wd. sensors are on the drivers side of the tranny, one forward and one in back. They are plastic housings, with a metal tab with one screw holding it in, and A wire coming off of it.

Looks just like the crank postion sensor. I would be if you pull them out, you would find metal particles stuck to them. Wipe them off and try them again. If they need replacing, they carry them at Autozone, Advance, O'reillys and other places.

Tim