No overdrive sometimes????

I was on a 1500 mile trip & on my way home yesterday I got about 325 miles from home & I had no overdrive. Sometimes it would go in, others not. I stopped it & restarted it a couple of times & it would be OK until it kicked out of OD on a hill. I also noticed that when I stopped I would sometimes get a hard banging shift between first & second. After about 200 miles I got a CEL. This happened about a year ago & the code was something to do with converter lock up or something like that. Anyway I got home OK. I disconnected the battery to clear codes & everything was OK. I drove it today around town & it was OK. Could this be a switch or control module???
Any thoughts or ideas???? I have a 1997 Blazer 4x4.
Thanks in advance.

Always get the code no before clearing code.
We need the code no?
That it is is throwing now.
Could be engine /transmission /speed sensor/or ign switch and or wiring.
Also 97 has a lot of ign switch problems

Yea, I know a code would of been nice, but I needed to drive it & the last time a year ago it did this the shop read it cleared it & told me it would be OK. Well it has for a year now. I drove it a hundred miles today & it worked flawless. So I guess I'll talk to a tranny shop & see if they can shed any light on it.
Thanks,

MT-2500, I took it to a transmission shop today & I told them exactly the same thing I described here & they told me the code number, & what was wrong. They also said it was the most common problem with 93-04 Blazers.
Since you were kind enough to at least respond & have helped me in the past, I'll share what they told me. It is a Valve in the Valve body that needs to be reversed. They said this will permanently fix the issue. I believe it locks the converter. I will confirm when they fix it on Wednesday. If a person continues to run it, without repair it will in time sometime short time burn the converter up, then it becomes a major repair.
Thanks for your time & response.

You are welcome and thanks for posting back how it went.
Also keep a eye on that ign switch.
Good luck

You are welcome and thanks for posting back how it went.
Also keep a eye on that ign switch.
Good luck

I'll give you a complete update after tomorrow when they fix it. I cross my fingers have been pretty lucky with this Blazer a lot of the common stuff hasn't given me problems YET.
I belong to a couple of auto forums & I hate it when a person posts a problem & nobody even says keep us posted I'm having a similar problem or anything. You have always been great about at least posting something back & I have seen that from you on many threads. If nothing else at least a person feels like some cares. I belong to a Ford Truck Forum & there are always people like yourself that respond in on way or another. I try to also respond as much as I can.
On the Blazer Forum I have talked to myself in 4 posts. The result is I won't post what the solution is on their board.
Again Thanks for your response & help you provide for us here. It is much appreciated.

thank you, for keeping us posted. somebody will prob have the same issues sooner or later. good luck, and let us know if you have any other problems.

thank you, for keeping us posted. somebody will prob have the same issues sooner or later. good luck, and let us know if you have any other problems.

As explained to me by the transmission shop. The problem was a valve in the Valve Body would leak by sometimes & when it did it would cause a line pressure increase which resulted in a hard 1-2 shift. With in pressure increase it would not let the trans to go into overdrive. So they reversed the valve. The shop called it a Valve Body Update. So that is what I was told. What I know is the transmission shifts 100% better. much smoother, no lag in between shifts. When you set the cruise after the trans shifts into overdrive it does kick back a gear then go back into overdrive like it has done since I bought this Blazer with 87,000 miles three years ago. It now has 164,000 miles. There are two things that a person should do that have an automatic transmission. One is add LubeGard to the fluid, & two is install a B&M SuperCooler. I have abused the crap out of this trans & I couldn't believe it when they dropped the pan & the fluid was not burned or dark. I have not changed the fluid in 65,000 miles. That is due to both of the things I just mentioned.
I hope this helps someone else. I can't believe the difference this fix made. Any good tranny shop will know exactly what they did to mine because I was told it was one of the most common fixes for the 4L60Es.

Thanks for the update. I'm familiar with the issue you experienced, but this is the first time (that I can remember) I've heard of it causing the transmission not to shift into overdrive. That's good to know. It appears that this issue can eventually trigger the PCM to set the transmission into limp mode.

Here's a little more info that I posted a few years ago:
http://www.automotiveforums.com/vbulletin/showthread.php?t=660483

Thanks for the update. I'm familiar with the issue you experienced, but this is the first time (that I can remember) I've heard of it causing the transmission not to shift into overdrive. That's good to know. It appears that this issue can eventually trigger the PCM to set the transmission into limp mode.

Here's a little more info that I posted a few years ago:
http://www.automotiveforums.com/vbulletin/showthread.php?t=660483

Thanks for the link. I was told that what I risked if it kept acting as it did was a burned up converter.
I'm not up to date with these computer operated transmissions. My days as a mechanic was with the TH350- TH400, FMX, C4-C-6s, 904/727. Powerglides etc.
I got out of the business when the 700R4 came out. I replaced about a half a dozen converters in the early days of them under warranty when I worked on the line for a Chevy dealer.
So I'm not completely sure how all this ties together with these 4L60Es but I do know that the transmission is 100% improved over when I took it in this morning. Even my wife noticed a difference when she drove it home. She is the daughter of a retired mechanic but she doesn't really pay that much attention. She knows if something is wrong & will always say something if she thinks something isn't right. But she is as most people she just drives the vehicles & trust me to keep them in shape. So for her to notice a difference right away says something. She thought it shifted much better. Which it does. But I noticed even more improvement.

it makes sense... high pressure can certainly keep it from locking up, and can certainly cause some massive damage to the torque converter. thanks for the update.

it makes sense... high pressure can certainly keep it from locking up, and can certainly cause some massive damage to the torque converter. thanks for the update.

I have drove it all day today & I'm impressed. It is like driving a different truck. If I would of known about this update I would of had it done a few years ago. It might of been some of the best money I have spent on this truck.:smile: