I am currently working on my son's 2001 2wd blazer. I bought it with the current transmission issue. It has reverse, 1st, and 4th. From hp tuners we have cycled the solenoids and can hear them actuate. When you take off it takes off in 1st and will shift into 4th after about 3k rpm after feathering the throttle a little. It stays perfectly fine in 4th and will downshift to 1st at the appropriate times. I have confirmed through the tuner that it believes it is shifting through the gears as it will display current gear and it changes as the solenoids cycle. I saw on this forum a post like mine but the final outcome was not posted. I believe user/moderator mrvedit said that a stuck solenoid a could cause this issue. Would I still hear the spool on the valve click if it were stuck? I have 2 new solenoids ready to install but I would rather have some more information before I waste a fluid change at least.

 

Unplug the round wiring harness that plugs into the passenger side of the trans. With this unplugged the trans should take off in 3rd gear. Some trans will have manual 2nd and will shift to 3rd when moving the shifter to 3rd. In 3rd gear both shift solenoids are turned off. By unplugging the harness, you will turn off both shift solenoids forcing the trans into 3rd gear. If no drive forward with harness unplugged the trans has a mechanical problem and will need to be taken apart.

 

I'll see about trying that this weekend. Thank you.

 

In 1st and 4th, Shift Solenoid "A" is ON; in 2nd and 3rd it is OFF. You say you can hear the solenoids activate, but a valve in the valve body could still be stuck. Saying that HP Tuners displays the correct gear makes it harder to explain, because the gear position is reported by the manifold pressure switch from the hydraulic pressures in the valve body.
Mr. Bond's suggested test is always very useful when diagnosing 4L60E problems. After that I would suggest dropping the pan and paying attention to the shift solenoids and the valves they control. In particular make sure that solenoid "A" has the strong spring pressure.
Since the trans works well in 1st and 4th, you are ruling out many/most internal problems. The troublesome 3/4 clutch must be holding and the band/servo must be holding; these are two of the most common problem areas.
Keep us posted and any questions coming.

 

Your comment on a post 11 years ago is what led me to believe a possible stuck solenoid a or weak/stuck spring. The original poster never said what fixed their issue. I work tomorrow but I'm off until Wednesday after that. One of those days I will be able to get the connector unplugged and see what it does. We also commanded second and third gear through hp tuners with no success.

 

OK I couldn't wait that long. Decided to run out and unplug the connector. It was forced into 3rd and drove in the gear.
I was able to manually shift into 2nd and it drove in it as well. I will be dropping the pan first chance I get to start an inspection l. I have never been inside a transmission but my friend with the hp tuners has replaced both a and b solenoids and a few other odds and ends on the 4l60.

 

Did you confirm by comparing speed and RPM that the trans was actually in 3rd and not in 4th?
If really in 3rd now, I am out of ideas on the next step. Perhaps someone else knows what is going on.\

 

I did not confirm through speed and rpm just by feel I guess you would say which could be wrong. I will verify with speed and rpm over my next few days off. Is there a possibility the return spring for one of solenoids is damaged? Or valve stuck but still able to hear it click once forced on? I'm pretty well stumped at this point.

 

Shift solenoid A the 1-2 solenoid is shorted to ground through solenoid housing and or wiring to the PCM causing always on condition. This will only allow 1st and 4th gear and since the shirts on the PCM side which grounds anyway not setting code.
Replace 1-2 solenoid check for damaged or shorted wiring in internal harness of even wires pinched between pan and case and if nothing there external harness to PCM or if nothing there PCM itself .
MOST LIKLEY either wires pinched between pan and case or solenoid armature shorted to ground .
This is the only logical way I can see to get a 1 to 4 shift ,
What I dont get is WHY NO CODES and HOW you hear a click . But I stand with the Solenoid A because you got 2nd and 3rd with harness unplugged.

 

Well I know why this seems so weird now. It appears I did not do enough due diligence before starting to research my issue. After verifying which gear I was in using rpm and speed I found that I have 1st and 3rd which is likely 2/4 band worn. Thank you all for working with me to try to figure this out. I went off what I was told when I purchased the blazer and didn't do enough proper checking beforehand.

 

Well that makes more sense. A worn out band denying 2nd and 4th is relatively common.
Measure servo endplay by pressing on the servo cover with a crowbar and holding a ruler next to it. Under 1/8" is spec, 3/16" is marginal and 1/4" indicates the band is worn on and 2nd and 4th gear are likely gone too.
Some members here have gotten a bit more life out of the trans by welding a little blob onto the end of the servo pin to reduce the endplay. Its a 24 year old trans, time soon for a rebuild.

 

Yes that makes much more sense, I was having to really think throew a way to get what you were describing , In fact spent a good part of the day thinking on how it was possible.