Printable View
Can't seem to figure out why my 4l80E is shifting rough after it warms up. It is on a 99 suburban w/7.4 liter k2500. I have given the engine a tune up. Flushed the Tranny fluid and filter change.
Thinking about new solenoids but haven't changed them yet?
Someone said MAF cleaning may help.
Once it cools down it will run smooth but freeway speeds after a while will shift out of overdrive and the RPMs will rise above 3K.
Stuck and need some advice.
Thanks,
Brian
bekmwan, welcome to the forum...:cheers:
When did this start happening...?
Are any DTC's present...?
By rough do you mean harsh...?
How harsh...?
At freeway speeds, it flares up...?
For a moment only, or does it lose forward drive...?
Have you checked the fluid level/condition immediately when this happens...?
This must of began about a month ago.
I have taken it in for codes and nothing was found.
As for the Harsh/rough... out on the freeway it was a smooth downshift or unnoticed downshift with the rise in RPM... But after that when coming to a stop at a stop sign it would down shift smooth but during excelleration from the stop sign you could feel the first shift be very "rough" is my word and it could have been a little later then normal shift but not sure on that. I don't see any "check engine light" come on.
I did pull over to check fluid and nothing was lost or low. After this check (a couple of day) I did the fluid/filter change but same issue.
Again at freeway speeds it would shift down and stay down but I wouldn't stay on the road long because I noticed it. I guess I could continue to drive it to see if it corrected itself but to nervious to ruin the whole thranny.
I wish there were some codes I could report back to you but they said nothing... Maybe I will take it to another place and see.
Thanks for the welcome and for the quick reply!
One possibility: check the IAT sensor wiring, it may be broken.
Well today I broke down and took the suburban to the chevy dealer to have them use their special tools to check out what is going on with my tranny. Codes P1870 was hit for tranny component slipping along with P0161 for O2 Sensor heater performance, bank 2 sensor 2.
The dealer suggests changing out the whole tranny at $3300 with a 3 year 100K warranty.
Local parts says $2500 with 18 month and 18K warranty.
I have to think through this one.
Thanks For the help and support!
I would get several more opinions quotes...
Where are you located...?
Did you check the IAT sensor wiring... sometimes one/both wires break (without throwing a DTC), the PCM sees the IAT as -39°F(-39°C) and goes to full pressure.
I took it to the chevy dealer for them to analyze and they came up with Code 1870. They and several others say change the whole tranny out... the cost is so large. But chevy has the best warraanty so I think that is the way to go.
I am in cedar city utah. Southern Utah