Code p0756 loss of power in first I changed shift solenoids no change. need advise.

sniderjr1

Original poster
Member
Nov 9, 2012
7
I Recently ran into a problem with my 05 envoy slt 4x4. It suddenly lost power in first gear. Seems sluggish and throws code P0756. So I changed both shift Solenoids and changed the fluid in the pan, but no change any advise about what might be going on or how to fix would be greatly appreciated. I've searched all over the internet. Same answer people coping and pasteing about its mechanical. But where to start after the change of the solenoid.
 

meerschm

Member
Aug 26, 2012
1,079
how many miles do you have?

did you clear the code after changing the solenoids?

you might want to download service manuals if you do not have one.
http://gmtnation.com/f23/need-service-manuals-get-them-here-371/

I found the following info on a different site (reference is a 5.7l, but the code logic should be similar)

Conditions for Setting the DTC

DTC P0756 sets if the following conditions occur:

Condition 1
The PCM commands first gear for 2 seconds.
The estimated gear ratio is 0 to 1.4.
The TCC slip speed is -3000 to 200 RPM.
All conditions are met for 1 second.

Condition 2
The PCM commands second gear for 1 second.
The estimated gear ratio is 0.9 to 1.2.
The torque converter efficiency is greater than 0.5.
All conditions are met for 2 seconds.

Action Taken When the DTC Sets

The PCM illuminates the malfunction indicator lamp (MIL).
The PCM commands 3rd gear only.
The PCM commands maximum line pressure.
The PCM inhibits TCC engagement.
The PCM inhibits fourth gear if the transmission is in hot mode.
The PCM freezes shift adapts from being updated.
The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
The PCM stores DTC P0756 in PCM history.

Conditions for Clearing the MIL/DTC

The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.
 

gmcman

Member
Dec 12, 2011
4,656
Did you change the filter?

If not, very likely that you can have a clogged or partially clogged filter restricting fluid flow.
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
Thanks for the replies and the information. My envoy has 115,000 miles. I did change the solenoids, filter, and fluid in the pan. I am going to try and reset. Then test drive. I'll post back. Hopefully I just forgot to reset.
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
No reseting did not work but on the road test i did relize that it seems the trans is not down shifting. I was going about 40 and manually tried to shift to 3rd then 2nd and then 1st no change in engine speed. Any suggestions. might be time to go to the trans clinic
 

meerschm

Member
Aug 26, 2012
1,079
how did you clear the code?


how long did it take to come back?
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
To reset I disconnected the battery waited a few minutes and the check engine light went out. I assumed this cleared the code. should I try another method?
 

meerschm

Member
Aug 26, 2012
1,079
another way is to use a scan tool to reset. I am not sure if the PCM history is cleared by disconnecting the battery, perhaps someone else can pitch in. how did you get the code P0756?

did the CEL stay off until you started to drive?

if so, I would think you cleared it. did you check for the code again, and verify it still has the P0756? not a different code?

if the problem is still there, and the wires look ok, next step is to look for blockage or sticking in the valve or passageway. stuff in the way, or the shift valve or shuttle valve could be stuck, or damaged seals on the solenoid valve.

you would have to pull the pan to look.

I know a few folks here have installed valve body kits, with good results.

I have not done this, and if it were me, I think I might consider taking someplace for a chat at least.
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
Thank you for the response. The check engine light was off for awhile until I took the vehicle up to about 55 then came to a stop. Ill check the wiring next time I open her up. Are the shift vavle and shuttle valve different than the shift solenoids A & B. Ive changed those already.
 

meerschm

Member
Aug 26, 2012
1,079
DTC P0756 5.7 L

this is pretty close to the I6 service manual, but not exact.

this place will sell you the whole valve body. I was going to order one, but decided I only needed a quart of fluid.

ACDelco High Performance 4L60E Valve Body With Solenoids | Trutechtrans.com

the solenoid pushes/pulls on the valves, which have to move in the valve body, changing the flow of fluid, which then operates the actual clutch and gear controls.

there are some instructions to use air to check valve movement, but I cannot find it at this moment.
 

dfc739

Member
Jul 29, 2012
170
Des Moines, IA
sniderjr1 said:
Thanks for the replies and the information. My envoy has 115,000 miles. I did change the solenoids, filter, and fluid in the pan. I am going to try and reset. Then test drive. I'll post back. Hopefully I just forgot to reset.

Which solenoids did you change? Only the two shift solenoids? Did you check the 3-2 downshift solenoid? You seem to have no problem upshifting (that's what the two shift solenoids do). It's the downshift that you are having trouble with. The "sluggishness" you are feeling might be the truck is still in an upper gear. There is an in-pan way to check these solenoids. They should have a certain resistance across them. The resistance values can be found here: http://www.eyeit.org/holden/4L60E Simple in Pan Maintenance.pdf

Also, I know it's expensive, but only use Dexron VI fluid. Even though the manual says it came with Dexron III, only use Dexron VI.
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
Alright took the pan off again and drained all the fluid. Had a hunch after all the good advise and took shift solenoid b off again and tried too take the shuttle vave out and the 2-3 shift valve. well I believe the problem is in the 2-3 shift valve because its stuck in the bore. trying diligently to get this thing out. may have to take the valve body off to do this. its stuck pretty good. moves about 3/4 of an inch then will not budge any tips?
 

sniderjr1

Original poster
Member
Nov 9, 2012
7
Ok so I took the valve body off which was intimidating at first. The 2-3 shift valve that was stuck in the bore had a piece off metal stuck between the body and the valve shaft. I also inspected the rest of the solenoid vales and found that the resistance across the 3-2 downshift solenoid and pwm/tcc solenoid were not within the parameters the post above showed. So I decided to take apart the whole valve body like a video on youtube by gear wrench showed. Then I degreased, washed, dried completley, then sprayed brake parts cleaner through out the whole body to get any water or oxidation sediment left over out of the body. I then reassembled each valve and new solenoid, reinstalled the freshly cleaned, semi rebuilt valve body to the transmission. Torgued everything to spec like the videos by gear wrench( I wish i was better at leaving short cuts for people to click) showed. Reinstalled the filter, new gasket, torgue the pan bolts, filled with VI ATF to the cold mark on the stick. I proceeded by erasing the check engine light. Then came the moment of truth started her up let warm to operating temp recheck the dipstick in neutral. Then ran through the gear selector feeling it pop in to each gear(p-r, P-d,). Then the road test. I reversed put the selector into drive and the envoy had power going forward. Continued onto second gear and obviously the fluid was still being worked through the tranny because it took high rpms to get into 3rd at first. So i ran through the gears and took it on a pretty grueling test drive. This vehicle I believe runs better than when i bought it used 5yrs ago. Thanks to all the responses and shortcuts everyone left they all helped. And to anyone who is a little mechanically inclined, the tranny valve body and solenoids were intimidating at first but it actually was really simple. Just rememer to take your time and remember where everything goes. And dont forget to torgue your bolts.
 

meerschm

Member
Aug 26, 2012
1,079
sniderjr1 said:
Ok so I took the valve body off which was intimidating at first. The 2-3 shift valve that was stuck in the bore had a piece off metal stuck between the body and the valve shaft. I also inspected the rest of the solenoid vales and found that the resistance across the 3-2 downshift solenoid and pwm/tcc solenoid were not within the parameters the post above showed. So I decided to take apart the whole valve body like a video on youtube by gear wrench showed. Then I degreased, washed, dried completley, then sprayed brake parts cleaner through out the whole body to get any water or oxidation sediment left over out of the body. I then reassembled each valve and new solenoid, reinstalled the freshly cleaned, semi rebuilt valve body to the transmission. Torgued everything to spec like the videos by gear wrench( I wish i was better at leaving short cuts for people to click) showed. Reinstalled the filter, new gasket, torgue the pan bolts, filled with VI ATF to the cold mark on the stick. I proceeded by erasing the check engine light. Then came the moment of truth started her up let warm to operating temp recheck the dipstick in neutral. Then ran through the gear selector feeling it pop in to each gear(p-r, P-d,). Then the road test. I reversed put the selector into drive and the envoy had power going forward. Continued onto second gear and obviously the fluid was still being worked through the tranny because it took high rpms to get into 3rd at first. So i ran through the gears and took it on a pretty grueling test drive. This vehicle I believe runs better than when i bought it used 5yrs ago. Thanks to all the responses and shortcuts everyone left they all helped. And to anyone who is a little mechanically inclined, the tranny valve body and solenoids were intimidating at first but it actually was really simple. Just rememer to take your time and remember where everything goes. And dont forget to torgue your bolts.

Congrats, sounds like you had a busy week.:smile:
 

dfc739

Member
Jul 29, 2012
170
Des Moines, IA
sniderjr1 said:
Ok so I took the valve body off which was intimidating at first. The 2-3 shift valve that was stuck in the bore had a piece off metal stuck between the body and the valve shaft. I also inspected the rest of the solenoid vales and found that the resistance across the 3-2 downshift solenoid and pwm/tcc solenoid were not within the parameters the post above showed. So I decided to take apart the whole valve body like a video on youtube by gear wrench showed. Then I degreased, washed, dried completley, then sprayed brake parts cleaner through out the whole body to get any water or oxidation sediment left over out of the body. I then reassembled each valve and new solenoid, reinstalled the freshly cleaned, semi rebuilt valve body to the transmission. Torgued everything to spec like the videos by gear wrench( I wish i was better at leaving short cuts for people to click) showed. Reinstalled the filter, new gasket, torgue the pan bolts, filled with VI ATF to the cold mark on the stick. I proceeded by erasing the check engine light. Then came the moment of truth started her up let warm to operating temp recheck the dipstick in neutral. Then ran through the gear selector feeling it pop in to each gear(p-r, P-d,). Then the road test. I reversed put the selector into drive and the envoy had power going forward. Continued onto second gear and obviously the fluid was still being worked through the tranny because it took high rpms to get into 3rd at first. So i ran through the gears and took it on a pretty grueling test drive. This vehicle I believe runs better than when i bought it used 5yrs ago. Thanks to all the responses and shortcuts everyone left they all helped. And to anyone who is a little mechanically inclined, the tranny valve body and solenoids were intimidating at first but it actually was really simple. Just rememer to take your time and remember where everything goes. And dont forget to torgue your bolts.


That's great news. So curiosity killed the cat... Do you still have the piece of metal you found stuck in the 2-3 shift valve? My opinion: that chunk of metal came from somewhere... which means something in there is missing a piece of metal. If you could take pics and post them, we might be able to identify it. But congratulations on saving yourself $$$$.
 

Reprise

Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
"We haven't had that member here since...2012" (homage to Felder / Henley / Frey)

I don't think you're going to get an answer from him. But if you want to see for yourself... enter your search term in google, with "site: youtube" on the end (w/o the quote marks)

I used brake cleaner on mine. A *mild* solvent would also work (the VB is aluminum, so no 'Purple Power').



On the phone with rebuilder, VB in my hand
"I want $5000 to rebuild your trans"
Well, you can go pound sand...
On my dashboard cluster, I saw the OBD light
My head grew heavy and my truck grew dim
I had to get it fixed, right


Then I looked up GMTNation, the guys there looked pretty swell
I joined up just so I could post, and said "hey, what the hell"
Then I noticed the post date, and I replied anyway
There were experts lurking on the site...thought I heard them say...


Welcome to the GMTNation
Such a lovely place, what a welcome space
Plenty of room at the forums for your question
Any model year, you can find it here


(All members... ) Should I finish the next verse? :dielaugh:
 
Last edited:

Forum Statistics

Threads
23,273
Posts
637,499
Members
18,472
Latest member
MissCrutcher

Members Online