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4T65e sudden finnickey 4-3 downshift. #4610838
12/22/17 03:59 AM
12/22/17 03:59 AM
Joined: Jan 2017
Posts: 507
Virginia
Hemispheres Offline OP
Hemispheres  Offline OP

Joined: Jan 2017
Posts: 507
Virginia
About a week ago I skidded off some ice in reverse at less than 10mph which left my front end in the ditch.

For about 45 seconds I struggled to get out. Applying the gas in R until TC kicked in while quickly steering side to side. Eventually I stopped moving after a few successful attempts to gain traction and almost made it out of the ditch and began spinning tires.

I panicked and at about 2k rpms I slammed the gear selector from R to 1 which gained me immediate traction and pulled me out of the ditch.

Trans seems to work just fine, but now Iím noticing at 80mph I canít get kick down to engage. However at 70 it engages and downshifts just fine.

Any idea what could be going on?


2009 Buick LaCrosse (3800 Series III) - 137,000 miles.
PZ Plat HM/Mobil 1 HM
Bosch/Purolator/Mobil filters
Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4610864
12/22/17 05:41 AM
12/22/17 05:41 AM
Joined: Jan 2013
Posts: 2,496
Texas
WyrTwister Offline
WyrTwister  Offline

Joined: Jan 2013
Posts: 2,496
Texas
What vehicle , engine , miles ? What does the fluid look / smell like ? Any loose wires vacuum lines ? Sensors ?


Wyr
God bless
Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4610907
12/22/17 07:26 AM
12/22/17 07:26 AM
Joined: Jan 2017
Posts: 507
Virginia
Hemispheres Offline OP
Hemispheres  Offline OP

Joined: Jan 2017
Posts: 507
Virginia
2009 Buick LaCrosse. 137k miles. Vehicle has been maintained fairly well. Fluid was changed a few months ago, has been changed once before. Shifts fine. No loose lines or sensors, no CEL.

Last edited by Hemispheres; 12/22/17 07:27 AM.

2009 Buick LaCrosse (3800 Series III) - 137,000 miles.
PZ Plat HM/Mobil 1 HM
Bosch/Purolator/Mobil filters
Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4610939
12/22/17 08:10 AM
12/22/17 08:10 AM
Joined: Aug 2005
Posts: 927
dayton oh
kc8adu Offline
kc8adu  Offline

Joined: Aug 2005
Posts: 927
dayton oh
disconnect the battery and force it to relearn.

Re: 4T65e sudden finnickey 4-3 downshift. [Re: kc8adu] #4611230
12/22/17 01:35 PM
12/22/17 01:35 PM
Joined: May 2016
Posts: 725
Canada
i_hate_autofraud Offline
i_hate_autofraud  Offline

Joined: May 2016
Posts: 725
Canada
Originally Posted By: kc8adu
disconnect the battery and force it to relearn.



Yeah, disconnect for an hour to make sure it clears the tranny computer.

However, to disconnect the battery, be sure it's 15 minutes after the key was taken
out of the ignition. There's GMs "RAP" "retained accessory power" if you disconnect within
15 minutes, the computers kick in a one-use Lithium primary battery associated with OnStar
system and drains it flat.

disconnect the battery cleanly, keep good contact while undoing clamp, then pull off in
one clean move or computers will interpret rapid electrical make-n-break of the ground wire
as an accident and kick in the lithium battery above. Same applies when you re-connect,
do it in one clean move without multiple make-n-break moves.

GM doesn't want you to know, they'd like to fix your OnStar!!

Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4611490
12/22/17 05:50 PM
12/22/17 05:50 PM
Joined: Jan 2017
Posts: 507
Virginia
Hemispheres Offline OP
Hemispheres  Offline OP

Joined: Jan 2017
Posts: 507
Virginia
That may be the issue. I disconnected the battery before leaving on my trip to reset fuel trims n get better mileage.


2009 Buick LaCrosse (3800 Series III) - 137,000 miles.
PZ Plat HM/Mobil 1 HM
Bosch/Purolator/Mobil filters
Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4613524
12/25/17 02:11 AM
12/25/17 02:11 AM
Joined: Jan 2017
Posts: 507
Virginia
Hemispheres Offline OP
Hemispheres  Offline OP

Joined: Jan 2017
Posts: 507
Virginia
Ok so Iíve done a relearn and now Iím getting harsh shifting under medium throttle. Iím talking thump when shifting. If itís done under light or wot it feels normal. This part of the shift adapt process?


2009 Buick LaCrosse (3800 Series III) - 137,000 miles.
PZ Plat HM/Mobil 1 HM
Bosch/Purolator/Mobil filters
Re: 4T65e sudden finnickey 4-3 downshift. [Re: Hemispheres] #4613554
12/25/17 04:43 AM
12/25/17 04:43 AM
Joined: Jan 2017
Posts: 507
Virginia
Hemispheres Offline OP
Hemispheres  Offline OP

Joined: Jan 2017
Posts: 507
Virginia
Well it looks like I busted my coolant temp sensor in the process of repairing more exhaust leaks. Iím reading that will cause and inoperative torque converter clutch which is most likely why Iím only having issues with upshifts.


2009 Buick LaCrosse (3800 Series III) - 137,000 miles.
PZ Plat HM/Mobil 1 HM
Bosch/Purolator/Mobil filters
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