The truck 6.5T 4x4 1 ton with 4L80E

Truck will shift into neutrial in 4 th gear at around 55 mph but always at 2500 rpm. If you turn off the truck while costing turn off the engine you gain all forward gears untill you hit 2500 rpm.

If the truck is in 3 gear (out of over drive same problrm is at 3000 rpm).

The same problem with or with out a load.
Troube codes are 16,73 and 87. Checked the speedo with a tech 2 scanner and checks ok. I hate to just throw parts at the truck.


The dealer has no clue

Thanks for any help.

Moved to the 4L80E section!

Do you have a tach gauge hooked up to a relay? Just kidding.
Both solenoids are fed through pin E going into the transmission
The 4L80-E controls lockup in 4th and in 3rd

1.Examine transmission fluid for good color and smell.
2. Check contacts going into the passthrough filter for contamination.
3. Drop the pan and check for debri, clogged filter, replace filter if clogged.
4. Pressure test the transmisison in all drive ranges. There is one pressure port on the driver's side.

The transmission is taking you out of lockup.
One reason why is the TFT sensor. Transmisison fluid temp sensor.
There is a table posted in the sticky on how to check it.
Check leads through the pass through connector.
I recommend using test pins you can buy at radio shack. The kind of pins that fit over the very fine pins in the transmissions connector.
Check the ohms against operating range to see if the sensor is skewed.
Check for obstruction in the transmisison oil cooling system.

I pulled a 7500 lb load with the truck on Sunday, keep the tack under 2500 rpm in third gear no problems.

Is there a code for high coolent temp? Having a hard time finding the thread could you help me out. Thanks

Radchevy I believe you are experiencing 4th gear hydraulic leaking within either the valve body or the pump. If you are going from 1st to 2nd into 3rd and 4th just spins..
Take it in to a techII scanner.

I for some strong reason believe that the fourth clutch assembly might not be receiving the pressure you need to engage.
Get a pressure gauge and hook it up to the transmission and take it for a test drive.
forward ranges to include the 4th gear should be ~100-120 at the top of my head.

I also believe that your Torque converter clutch should be engaging. I would PM mikeL just to be sure.

Ok if I have a leak down in forth gear is this worn seals?

Still driving the truck just staying below 60 mph. Not sure if the driving the truck will affect the current problem.


The converter is locking up I can feel it and see it on the scanner. Although the converter is loose and stalls around 2300 rpm. I would to have the stall lowered to 1700 rpm.

This is one Area that is not my forte' taking off the valve body and applying air pressure to determine if the 4th clutch is applying.
I will tell you what the achilles heel of the 4L80-E transmission is. that's the TCC solenoid valve. That valve sends a signal to the "shift control valve. Wet air tests are done to determine if the valve and it's bore are worn. If at fault then the tranny has a problem in shifting into mechanical lockup.

I will tell you this. The 1-2 and the 2-3 shifting valves when engaged send pressure to the 4th clutch. If you need to determine if it is a valve body problem vs a clutch problem. I heard somewhere else that the 4L80-E is problematic at the 4th clutch in pressure delivery to the clutch.

Found out what was the problem was.

The rear speed sensor would drop out just enough to kill the trans but the speed0 would still work.

Vehicle speed sensor might have been causing the computer to take it out of lockup mebbee??

Neutral? Now I am in neutral..