4L80e goes into limp mode

[bhelms22]

I just bought a 2000 K2500 Classic with the 454 and 4L80e. After a few months the tranny acts like it is going into limp mode. It has only happened running on long trips and I can not make it happen on command, it seems random. When pulling a steep hill sometimes it will downshift and not go back into overdrive. Then when you stop/have to get back up to speed it shifts hard from 1-2 and 2-3. If you pull over and unplug the battery for a few seconds it will go back to normal and shift perfectly.

Tranny fluid looks good/full, not throwing any codes when it goes into limpmode ,or at least the SES light does not come on. Sorry if there is any spelling errors but typing on a toughbook is like driving a car with no powersteering. Thanks in advance for any help.

 

[WarWagon]

Why would a "service ENGINE soon" light come on for a transmission problem? Hint: It doesn't!

Likely you are slipping the TCC and setting a slipping code. An oil change may buy you some time as well as rebuilding the valve body TCC from wear.

Next time it limps pull the codes - code readers are cheap. Or just have the trans checked and overhauled.

 

[bhelms22]

As I said it is not throwing any codes.

 

[Suburbank2500]

Could be you have high oil pressure in the tranny, this should be checked out so you dont break any hard parts.
If it shifts ok after disconnecting the power you probably have DTC codes of some kind..

 

[THEFERMANATOR]

As I said it is not throwing any codes.

Have you put a scanner orcode reader on it when it does it? You said it doesn't turn the SES light on, but that does not mean it is not throwing any codes. Since it's a 2000 it's OBDII which is pretty good about turning the light on for all problems, but there are still alot that won't turn it on. If it is defaulting to max line pressure(which it sounds like from your description of harsh shifts), then there is a REALLY good chance it will be throwing a pending code. Pending codes will not turn the light on, and must be read when the problem is happening as they will clear out on the next drive cycle if the fault doesn't occur again. Also your TPS could be going bad and cause it to shift hard and late, not go into overdrive, but many times will not set a SES light. Also being it's a 2000, it probably has a MAF sensor. And if there is any dirt, debris, or oil residue on the MAF it can cause all kinds of havoc with how it shifts.

You NEED to get a scanner on it when it does this to see what it is seeing, and then what it is commanding to know what it is doing.