Hello, New to this board.
I have 2000 Chevy Silverado with the 4L80-E transmission 6.0L motor. A little while back I noticed that it was not switching into overdrive on the highway, as usual at 100km/hr it running around 1900 rpm, now it was at 2500 rpm, an engine speed that is usually common in 3rd at 100km/hr. When I removed my foot from the accelerator, it would shift into overdrive as the rpm's would drop right away, as soon as I applied the slightest bit of pressure on the accelerator, it would shift down to 3rd as evidence of the rpm increasing. Took it to a mechanic friend of mine and there was a code that pointed at a torque conv. problem, but he was not sure as his experience was very little with this type of trans. He did suggest to disconnect the battery and cancel the code and try and see if this would reset the trouble code and enable the trans to shift into od, did not work. Next I took the trans to the dealer and to make a long story short, the technician said that there was no code present, but it looked like all indications were pointing at a fried torque conv. I proceeded to order a torque conv. and install it myself. This is were I am at, new tc, same problem, not a bit of change, obvious that the tc was not the problem. Just one addition to the story, the trans oil was slightly discolored, slightly browny tinge, when the I removed the pan , there was not any heavy sludge, just a slight grey sludge coating the bottom of the pan, and not any metal particles on the magnet. Any help would be great, I am not sure at this stage what needs to be done or looked at. Thank you......Joey

I would drive the truck and recheck codes.


Solenoid locations
http://www.dieselplace.com/forum/showthread.php?t=217766

Checking pins
http://www.dieselplace.com/forum/attachment.php?attachmentid=54295&d=1200617268

To check for a skewed sensor go here
http://www.dieselplace.com/forum/showthread.php?t=327063

The TCC solenoid is the little part that the computer sends a signal to.
The signal is then sent to the pump to the TCC control valve and it gets operated by pressure.
The problem is that the TCC solenoid has a close tolerance between the valve and the bore. The achilles heel of the GM transmission family with the TCC solenoid is the wear that develops between the valve and the bore. When leakage occurs the hydraulic signal becomes too weak to operate the control valve.
Damage to the torque converter can happen when slippage occurs between the piston and the torque converter itself because of the heat buildup.
If your torque converter will not engage into Overdrive then you have to pull codes. Its important to remember to record codes before erasing them. If the computer will not give you a code then drive until one comes around provided the Torque converter doesn't heat up too much.

Note if your transmission is shifting harder than normal.

Examples of why the computer refuses to allow TCC lockup.

Transmission too hot. Or a bad (skewed sensor) transmisison fluid temp sensor.
Transmission component slipping. Usually noted when the slippage occurs with the torque converter.
A bad Vehicle speed sensor
A bad transmission output speed sensor.
A bad Transmission pressure manifold gauge causing havoc.
A Bad throttle position sensor.

When a mechanic gives you advise without checking codes or going over the truck I would throttle him.

Get some codes out of it and come back.

Well, the 2000 4L80E converter is known to have problems. I had to replace mine as other have.

I had a mechanic recheck for codes today, found none. Checked for brake switch operation, engine temp sensor and tps sensor all checked out good. On the test drive we went through full stop to highway speed and in a nutshell there is no lockup at the overdrive position, as I kept my foot on the accelerator, I applied slight brake pressure, I assume there should be a noticeable increase in rpm, all other gears were strong on the shift and worked as it should. With there being no fault codes, can I assume it is a mechanical issue ? Thank you for your input....Joey

I had a mechanic recheck for codes today, found none. Checked for brake switch operation, engine temp sensor and tps sensor all checked out good. On the test drive we went through full stop to highway speed and in a nutshell there is no lockup at the overdrive position, as I kept my foot on the accelerator, I applied slight brake pressure, I assume there should be a noticeable increase in rpm, all other gears were strong on the shift and worked as it should. With there being no fault codes, can I assume it is a mechanical issue ? Thank you for your input....Joey

The TCC doesn't unlock when you press the brakes on a 4L80E in the 99-2003 model years. Not sure about the others, but that part is normal. When I was dealing with my problem (bad TC) I kept thinking it would, but it doesn't. That's the way it works normally but it led me in the wrong direction for a bit.

My tc is not locking up, and the mechanic is telling me it's the brakes.
I have a brake light on the dash, and the computer is holding it out of lockup. ( I'm pretty sure, the front calipers are sticking, so I'm gonna replace them today) mine is a 92 though...
the codes are saying it's the brakes holding the TC out on mine.

I am fairly certain there is a mulitpurpose brake switch. One portion of the switch takes it out of OD. If the switch is bad or misadjusted check it out.
It is electrical.