After a full rebuild, I got a solenoid code “P0756 2-3 Shift no first or second gear.” I THINK this was due to the tranny being about 1.5quarts low, because I reset the code and it did not come back.

Now, upon the test driving, it appears I have no second gear (and possibly 4th - will get to that in a sec). It will run to 2500-3500rpm in first then shifts to 3rd (shifts easier if I let up on the gas). Also, when it shifts it somewhat feels like it going into 2nd for a split second.

Manually shifting does not help. External wiring seems fine. I tested the servo end play to be about an 1/8”. Of course I changed the band, the reverse input drum was not visibly worn, both solenoids replaced (including the pwm and tcc) also installed a remanufactured torque converter.

Here is why I am not sure if I have overdrive: I am pretty sure the vehicle went into “limp mode” due to a rare and sporadic/reoccurring knock sensor code that I will address later. This made it run like @$$ from stop to go (of course this happened on my very short 4th gear testing). Anyways, given my meager understanding of transmissions I am afraid to drive it at all to retest in fear I might damage something.

I was about to take the pan back off and test the solenoid and wiring as well as to verify the valves behind the solenoids are not stuck or installed backwards somehow (which I checked twice on rebuild), but I am beyond annoyed with this project and likely will break something or hurt myself. And I don't think that would explain 4th. So here I am

Can anything there anything else do this?

The rebuild was done due to loss of 4th and reverse. The only “hard part” I found damaged/worn/broken was the drive shell.

 

What is the Production Year of the Transmission (Post the Broadcast Code Sticker if you are unsure)?
Is this a 4L60E Transmission, or a 4L70E Transmission with an Input Speed Sensor?
The Sun-Shell/ Reaction-Shell was damaged, resulting in NO Reverse, 2nd, and 4th Gear-Ranges... Correct?

What is the Year, Make, and Model of the Vehicle?
Is the Vehicle Stock or Modified?
If Modified; what was changed (Engine, Differential, Etc...)
Did the Final Drive Ratio or the Tire Height significantly change?
Did this Vehicle originally come with a 4L60E Transmission?
Was the Transmission just overhauled back to Stock... or modified/ upgraded in any way?

What are all the Power-Train DTCs/ Codes (Engine Codes for example, can affect the Transmission)?

Limp-Mode will generally have the Transmission operate in whichever Gear-Range that does not use any of the Shift Solenoids.
In this situation, that would be 3rd-Gear... as Both of the Shift Solenoids are OFF for 3rd-Gear.

Power-Train Control Module Diagnostic Trouble Code P0756 pertains to 2-3 Shift Solenoid Behavior/ Performance/ Malfunction Detected.
This is NOT an Electrically related condition for the 2-3 Shift Solenoid... Normally a physical/ mechanical issue is at hand for this DTC (unless additional DTC are set for the Shift Solenoids electrical circuits).

P0756 will NORMALLY set when the PCM is commanding 1st-Gear or 2nd-Gear (depending on vehicle speed and throttle input), but instead the Transmission goes through a 4th-3rd-3rd-4th Shift Pattern.

Depending on your answers to my questions... This issue may be a circuit leak, Valve-Body issue, or an incorrect component used...
There are many other possibilities depending on the answers you provide...
So answer them, and we will continue.

 

Oops! I am fairly confident that this is the original transmission: 2002 (sorry I do not have access to the sticker atm).

Definitely 4L60E and I hope this doesn't get me in trouble as I just now realized this is more of a car-based forum. This is a 2002 Silverado z71 (4x4). But it is the same stuffs, just different back connector flange thing.
I don't recall 2nd going out. It was driven 20 min on the highway with I guess 5 stops to the house and immediately parked.

Fairly stock, I am not the original owner and I sometimes wonder if the computer was tweaked, but other than that, no.

No.
Do not know how to check this without some sort of VIN lookup, but yes?
Almost completely to stock. Some plastic things swapped with aluminum parts (I think the servo piston things I can get back with you on that...supposedly common failure points). And there was a sommex part I modified that required a 100.00 reamer on the valve body. I forget what it is called. The only hard parts changed were the drive shell and the torque converter.
P0756: Cleared and has not come back after ~30min of test driving.
P0332: Knock Sensor 2 Circuit Low--cleared and has not come back (this is a rare and seemingly random issue with this vehicle)
I am not entirely sure it was in limp mode. Something was causing severe lack of acceleration when going from a standstill. Like I said, I am afraid to drive it any further and risk damaging anything that would require pulling the transmission. I am hoping I can rectify this in the valve body area.
??
I don't follow. How can it not be eclectically related? If it is not, how is the PCM (or whatever) reporting the code?
And I don't understand what you mean by 4th-3rd-3rd-4th Shift Pattern. (Apologies if I am being dense.)

Should I try to test for 4th again? Or is that too risky? I know I put this thing together, but I have yet to wrap my mind around how it all works in practice.

Thanks for your thoughtful response! And I hope I answered everything adequately.

 

I guess my response will not get approved.

Almost everything is stock. 2002

 

Hey guy!

I don't just type all this stuff at 3 AM for my health.

If I put in the time to try and help you...
you could at least try and answer the questions.

 

I am very sorry.
I was exhausted when I responded.
Thankfully, I kept a document at work with my I original response (with a few updates):

Oops! I am fairly confident that this is the original transmission: 2002 (sorry I do not have access to the sticker atm).

Definitely 4L60E and I hope this isn’t an issue--I just realized this is more of a car-based forum. This is a 2002 Silverado z71 (4x4). But it is the same stuffs, just different back connector flange thing.
I didn't notice 2nd being out. It was driven 20 min on the highway with few stops to the house and immediately parked. But definitely no 4th or reverse. It was a little odd though how it all happened because the driver gunned it a little from a standstill...there was a noticeable clunk, noticed no 4th on the way to go eat. Then later noticed no reverse when I was half smashed leaving Chilis. That was fun getting it out of the parking lot...lol

Fairly stock, I am not the original owner and I sometimes wonder if the computer was tweaked, but other than that, stock to my knowledge. I had to do the pumpkin seal on the diff and front seal a while back. Looked stock to me.

No.
Do not know how to check this without some sort of VIN lookup, but I pretty sure is came with the 4L60E stock.
Almost completely to stock. Some plastic things swapped with aluminum parts that came with the kit. There was a sommex part I modified on the valve-body that required a 100.00 reamer. I forget what it is called. I can get the part if needed.
P0756: Cleared and has not come back after ~30min of test driving.
P0332: Knock Sensor 2 Circuit Low--cleared and has not come back (this is a rare and seemingly random issue with this vehicle)
UPDATE: after about 100 miles (nearly all highway) the check engine light is back on will update once I am able to scan it.
I am not entirely sure it was in limp mode. Something was causing severe lack of acceleration when going from a standstill. Resetting the comp/pcm/ecu or whatever cleared it up--pretty sure the "P0332: Knock Sensor 2 Circuit Low". I (was) afraid to drive it any further and risk damaging anything that would require pulling the transmission, but against my wishes there are now about 100 more miles on it. I am hoping I can rectify this in the valve body area or something else like speed sensors or some other some of the other seemingly nonsensical stuff I have been reading.
Can you clarify this?
I don't follow. How can it not be eclectically related? If it is not, how is the PCM reporting the code (not arguing, I simply don't understand)?
Not sure what you mean by "4th-3rd-3rd-4th Shift Pattern" because I am almost sure there is no 4th at all. However, the highway cruising RPM is seems identical compared to before the rebuild.

Thanks for your thoughtful response! And I hope I answered everything adequately.

 

I answered everything... hopefully a mod will approve my message ż

 

what are you talking about?
there isn't approval for posts on the forum here

if you responded...it will show up just like this response I am typing now

 

Because I am new to this forum (less than 10 posts)....this is what the forum is telling me. I don't know why posts with only one quote/short posts are going through.

I will try to PM you if that is ok?

 

yes ok

 

I have no idea why my posts were not approved. I guess the admins are swamped or something.
I even posted a few more times and the forum still shows I only have 4 posts.

And because I am not a big boy on the forum, I cannot even send PMs it seems. Send me a pm so i can respond or email me at synauxcc@gmail.com....

I swear I am not trying to be difficult

 

If you can type here, then just retype the answers to the questions that I asked you.

 

you've responded here more than once complaining...that you can't post here

it makes 0 sense

if you can't figure out how to work the forum, idk what to tell ya

 

Been offline for a few days... However, I am not complaining, but what makes zero sense is why my post was not approved or disapproved (twice) and why I cannot send PMs.

Regardless, I will attempt taking the original post and split it up is sections:

Oops! I am fairly confident that this is the original transmission: 2002. Where is the sticker located? I couldn’t seem to find it.

Definitely 4L60E and I hope this isn’t an issue--I just realized this is more of a car-based forum. This is a 2002 Silverado z71 (4x4). But it is the same stuffs, just different back connector flange thing.
I don't recall 2nd going out. It was driven 20 min on the highway with very few stop to the house and immediately parked.

Fairly stock, I am not the original owner and I sometimes wonder if the ECM was tweaked, but other than that, stock to my knowledge.

 

No.
Do not know how to check this without some sort of VIN lookup, but I pretty sure is came with the 4L60E stock.
Almost completely to stock. Some plastic things swapped with aluminum parts (I think the servo thing, basically the same part). There was a sommex part I modified on the valve-body that required a 100.00 reamer. I forget what it is called. I can get the part if needed.
P0756: Cleared and has not come back after ~30min of test driving.
P0332: Knock Sensor 2 Circuit Low--cleared and has not come back (this is a rare and seemingly random issue with this vehicle)
I am not entirely sure it was in limp mode. Something was causing severe lack of acceleration when going from a standstill. I (was) dfraid to drive it any further and risk damaging anything that would require pulling the transmission, but against my wishes there are now about 100 more miles on it. I am hoping I can rectify this in the valve body area are.
??

 

I don't follow. How can it not be eclectically related? If it is not, how is the PCM (or whatever) reporting the code?
And I don't understand what you mean by 4th-3rd-3rd-4th Shift Pattern.
I am almost sure there is not 4th at all, but the highways cruising RPM is seems identical compared to prior rebuild.

Thanks for your thoughtful response! And I hope I answered everything adequately.

Well, I don't know why all this wouldn't post as one long message but it is on here now!

 

Lets say that you have an Automotive Floor-Jack:

Hydraulic fluid moves the arm of the Floor-Jack, when the lever is pumped.

However, the Floor-Jack has two sensors and a computer that monitors the position of the Floor-Jack Arm.
One sensor at the very bottom of the Jack Arm travel, and one sensor at the very top.
This way the computer can process data of the Jack Arm being all the way up, or all the way down.

Lets say that you are pumping the Jack Arm up as far as you can get it...
But the Jack Arm does not make it all the way to the top of its travel.
You look for computer codes and find one saying that the top sensor does not read the Jack Arm as at the very top position.

There is nothing wrong with the sensor, even though there is a code related to the top sensor.
The problem is hydraulic, preventing the Jack-Arm from going all the way up.

This same theory applies to how Automatic Transmission monitoring occurs.

 

That makes a lot of sense. Thank you.
So is it possible I installed the valve backwards or something for solenoid B?

But even if I did, I imagine the code would come back (which it hasn't).

Any idea what might be the root issue?
Another thing I noticed is if you punch it on the highway it shifts to first. And when it does this (not always and I might be delusional) it feels like it slides into 2nd first for a split second same for 1st to 3rd, but it is very subtle and very quick.

Are these things worth considering: Wiring harness, ecu, speed sensors, perhaps one of the three sensors swapped on the diff (all have the same connector, I believe)?

Thanks

 

And and... I bought an after market solenoid that goes into the pump (called the TCC solenoid, I believe), because the old one broke.

It had some odd crimp connectors. If my research is correct, if those connections weren't crimped correctly that could explain no 4th (but doesn't explain no 2nd), correct?

 

How many miles has the vehicle been driven since the Diagnostic Trouble Codes were cleared.
Depending on the conditions in which the vehicle was operated (driven), the period of time required for the Diagnostic Trouble Codes to return may take a long time.

Has the vehicle been driven on the expressway or regular roads? Both the expressway and regular roads?
The DTCs can take hundreds of miles to return depending on the driving conditions.

The PCM is constantly monitoring data from all of the Power-Train sensors.
However the DTCs are not set from the PCM processing all of the sensor data...
This is because originally the CPU and RAM of the PCM were too slow to process all of the sensor data simultaneously.
Today the PCM could actually do this, however the PCM does not.

So, going back to the start of OBDII in 1996... these slow operating PCMs had to have another way to take processed data for an individual sensor, or sometimes a group of related sensors... and determine if any DTC needs to be set.
The way that this was achieved was for the PCM to complete a series of self-tests on the sensors, or sensor groups one at a time.
The number of self-tests varies from vehicle to vehicle... but there are usually 4 to 12 tests to be completed.
The different tests are completed under different driving conditions... and done one at a time.

So unless you have access to a DTC scan-tool or computer program to look at the PCM data and test information...
to be patient in waiting to see of the DTCs return.
Generally if the vehicle is not operating normally... then there is a very good chance that the DTCs will return.

In regard to what the issue actually is... I am going to reference my prior statement:
"DTC: P0756 pertains to 2-3 Shift Solenoid Behavior/ Performance/ Malfunction Detected.
This is NOT an Electrically related condition for the 2-3 Shift Solenoid... Normally a physical/ mechanical issue is at hand for this DTC (unless additional DTC are set for the Shift Solenoids electrical circuits)".

Most likely there is a hydraulic or mechanical issue.
Unless you feel that you are capable of disassembling and diagnosing the Transmission on your own...
I would bring the vehicle back to the Business/ Shop that rebuilt and installed the Transmission for you.
Good luck.