4L60E, now a new Shifting Problem in '99 Suburban

[V-8Fan]

This recent thread describes what I went through a couple of weeks ago:

http://www.automotiveforums.com/vbul....php?t=1087466

At the conclusion of that thread, the problems were gone. In a matter of just a couple of days, the 2 to 3 shift flare problem reappeared.

If I accelerate gently and keep the rpm down to about 2500 or less, I get a normal shift from 2 to 3 and I can then accelerate with vigor without any apparent problem.

If I accelerate the way I normally drive, at the 2 to 3 shift point the transmission misses the shift and I have to let off the throttle for a few seconds and wait for 3rd to engage. I usually see no codes, but once in a while P0758 reappears.

Both solenoids A and B have been replaced, as described in the thread referenced above.

More symptoms, and maybe this is a vital clue: the 3 to 4 shift is fine, but I've noticed that lockup takes a while to occur. When locked up, I normally see almost exactly 2000 rpm at 70 mph. I am seeing about 2150 rpm at 70 mph until lockup finally takes place, but I can't say exactly when it does happen---I have to watch the road now and again.

Could I have another bad solenoid? I really don't think there are any bands or clutches going out because once they engage properly they seem to hold up to the torque. Could it be something other than one of the other solenoids? I understand there are a 3-2 solenoid and a pressure control solenoid, but I don't know enough about their purposes to decide that either needs to be replaced.

[MT-2500]

Originally Posted by V-8Fan

This recent thread describes what I went through a couple of weeks ago:

http://www.automotiveforums.com/vbul....php?t=1087466

At the conclusion of that thread, the problems were gone. In a matter of just a couple of days, the 2 to 3 shift flare problem reappeared.

If I accelerate gently and keep the rpm down to about 2500 or less, I get a normal shift from 2 to 3 and I can then accelerate with vigor without any apparent problem.

If I accelerate the way I normally drive, at the 2 to 3 shift point the transmission misses the shift and I have to let off the throttle for a few seconds and wait for 3rd to engage. I usually see no codes, but once in a while P0758 reappears.

Both solenoids A and B have been replaced, as described in the thread referenced above.

More symptoms, and maybe this is a vital clue: the 3 to 4 shift is fine, but I've noticed that lockup takes a while to occur. When locked up, I normally see almost exactly 2000 rpm at 70 mph. I am seeing about 2150 rpm at 70 mph until lockup finally takes place, but I can't say exactly when it does happen---I have to watch the road now and again.

Could I have another bad solenoid? I really don't think there are any bands or clutches going out because once they engage properly they seem to hold up to the torque. Could it be something other than one of the other solenoids? I understand there are a 3-2 solenoid and a pressure control solenoid, but I don't know enough about their purposes to decide that either needs to be replaced.

You need to get it on a transmission capable scanner and check for codes and read out transmission and shift data and any engine codes.
Post back any codes.

[777stickman]

The P0758 code indicates an issue with the 2-3 shift solenoid. Could be the unit itself or wiring or VCM.

[V-8Fan]

As per solenoids A & B, both have been replaced. I don't want to rewrite all I've done and been through; it's all in the previous thread mentioned above.

The only code I am seeing is P0758. My scanner is an Innova 3100c. I am not sure whether this is the type of code reader being recommended or not.

Fiddling around this afternoon, I took the vehicle out for some testing. I did not realize before today, but once the code P0758 is thrown and the transmission is forced to operate in limp mode (2nd & 3rd only), the 2nd to 3rd shifts are positive and firm. Surely this means something, but it's over my head. It does seem to me to indicate that there is nothing wrong with clutches, bands, and the like and that it's just a malfunction within the valve body. But I don't know...that's why I am here!

If I could find a decent elementary description of what happens with the various solenoids during shifting, I'd study it. I have found no such resource.

[MT-2500]

Originally Posted by V-8Fan

As per solenoids A & B, both have been replaced. I don't want to rewrite all I've done and been through; it's all in the previous thread mentioned above.

The only code I am seeing is P0758. My scanner is an Innova 3100c. I am not sure whether this is the type of code reader being recommended or not.

Fiddling around this afternoon, I took the vehicle out for some testing. I did not realize before today, but once the code P0758 is thrown and the transmission is forced to operate in limp mode (2nd & 3rd only), the 2nd to 3rd shifts are positive and firm. Surely this means something, but it's over my head. It does seem to me to indicate that there is nothing wrong with clutches, bands, and the like and that it's just a malfunction within the valve body. But I don't know...that's why I am here!

If I could find a decent elementary description of what happens with the various solenoids during shifting, I'd study it. I have found no such resource.

The code is a solenoid or wiring problem.
Code P0758 is a short or open to the solenoid.
When code is set transmission goes into limp mode.
Get a All Data DIY online subscription and it will led you threw repair.

[V-8Fan]

I know what P0758 is supposed to be according to the diagnostic information. Apparently it is not so cut and dried.

[maxwedge]

There is a specific trouble tree for any code, this is the key to proper diagnosis as MT2500 stated an oe manual or an Alldata subscription is the way to go to pin down a complex problem.

[V-8Fan]

Today I replaced the A & B shift solenoids (again), the 3-2 solenoid, the PWM solenoid, TCC solenoid, force motor, the pressure switch, and the harness. All the stuff came in a reasonably priced kit (about $135).

The same symptoms persist: once it throws the P0758 code and the trans is in limp mode, the 2 to 3 shifts are positive and firm, even though they do seem to be just a little bit late under hard acceleration. When I clear the code and run in D the missed 2 to 3 shift reappears.

I'm now going to pull out the rest of my hair.

[MT-2500]

Originally Posted by V-8Fan

Today I replaced the A & B shift solenoids (again), the 3-2 solenoid, the PWM solenoid, TCC solenoid, force motor, the pressure switch, and the harness. All the stuff came in a reasonably priced kit (about $135).

The same symptoms persist: once it throws the P0758 code and the trans is in limp mode, the 2 to 3 shifts are positive and firm, even though they do seem to be just a little bit late under hard acceleration. When I clear the code and run in D the missed 2 to 3 shift reappears.

I'm now going to pull out the rest of my hair.

After or before you do that.
Read post no. 5 and no. 7

[V-8Fan]

MT-2500, I'm willing to do that but what I'd like to know first is whether the subscription is really useful to someone who doesn't own a lot of testing equipment and diagnostic tools. I'm always willing to twist a wrench but I don't need to keep this vehicle and don't want to invest a lot in it. Is this geared toward the home mechanic?

[MT-2500]

Originally Posted by V-8Fan

MT-2500, I'm willing to do that but what I'd like to know first is whether the subscription is really useful to someone who doesn't own a lot of testing equipment and diagnostic tools. I'm always willing to twist a wrench but I don't need to keep this vehicle and don't want to invest a lot in it. Is this geared toward the home mechanic?

Why do you think it is called a DIY subscription.
Lot cheaper that the couple hundred you have already spent without fixing it.
Go threw the repair flow chart for your code.

[j cAT]

Originally Posted by V-8Fan

This recent thread describes what I went through a couple of weeks ago:

http://www.automotiveforums.com/vbul....php?t=1087466

At the conclusion of that thread, the problems were gone. In a matter of just a couple of days, the 2 to 3 shift flare problem reappeared.

If I accelerate gently and keep the rpm down to about 2500 or less, I get a normal shift from 2 to 3 and I can then accelerate with vigor without any apparent problem.

If I accelerate the way I normally drive, at the 2 to 3 shift point the transmission misses the shift and I have to let off the throttle for a few seconds and wait for 3rd to engage. I usually see no codes, but once in a while P0758 reappears.

Both solenoids A and B have been replaced, as described in the thread referenced above.

More symptoms, and maybe this is a vital clue: the 3 to 4 shift is fine, but I've noticed that lockup takes a while to occur. When locked up, I normally see almost exactly 2000 rpm at 70 mph. I am seeing about 2150 rpm at 70 mph until lockup finally takes place, but I can't say exactly when it does happen---I have to watch the road now and again.

Could I have another bad solenoid? I really don't think there are any bands or clutches going out because once they engage properly they seem to hold up to the torque. Could it be something other than one of the other solenoids? I understand there are a 3-2 solenoid and a pressure control solenoid, but I don't know enough about their purposes to decide that either needs to be replaced.

with the erratic shift condition and the age / use I would see if the 12 volts to the transmission from the ignition switch is good. sometimes on vehicles this old the contacts on the ignition switch or the wiring into the tranny is the problem. sometimes its the connection to the internal solenoid not secure.

[V-8Fan]

Now this is funny...


I let the Suburban sit in my driveway and didn't touch it for several months. I decided to get rid of it and let someone else fool with it, so I went out to start it and the battery was dead as a doornail. No surprise there. The surprise is that the shifting problem and the codes are history.

Evidently just clearing codes was leaving something untouched in the computer, but totally resetting the computer wiped it out, whatever it was. I've put a few miles on it and made a few trips---no problem whatsoever.

I'll never know for sure, but I suspect the mechanical issue was addressed the first time I changed out the solenoid.