I have a 97 4x4 automatic with 210000 miles. The tranny does not go into overdrive and when starting off from dead stop seems that tranny slips somewhat then starts shift regulerly till od supposed to kick in. Any idea where I should start looking. Fluid and filter has been changed.

 

Does it do this when its warm and cold?

 

It does warm or cold. Found trouble codes started to pop up,p1870, p740,p753, p758, p1860 and p785.Besides minor mechanical and normal maintnance truck has been excellant and would like to keep it.

 

Did you change the fluid and filter yourself?
Did you see any debris or fine material in the pan?

I guess a shop would say something as they would have tried to sell you a rebuild or something....

Either way, the stuff in the pan would go a long way towards diagnosis.

 

try this, on the front of your motor, by the thermostat housing disconnect the temp sending unit.. see if this allows it to go into overdrive. i have this vey problem and have found that the trans goes into a warm state when this is disconnected. util i found out why i have been dealing with the engine service light. i did have an initial problem in the trans. my mileage dropped to 10 mpg and i lost overdrive and tcc. i removed the pan and changed filter and fluid. while i had the filter off i reached up and gave the shift solenoid and tcc solenoid a push only to find they stuck, probably just a piece of grit. any way, once they were unstuck it shifted fine. however, i live in central MI and winter is here. i am currently running with my temp sending unit unplugged so overdrive engages. hope this helps if only for a short time.

 

Tried them didn,t work. I searched internet and found a TSB on it. It said to check voltage at fuse box for trans. circuit while ignition was on. Check and it was 7.5v. problem was in the ignition switch. Figured since I needed a new one no harm in looking inside. Found burnt and dirty contacts. Very cheaply made, I guess that is why they have a TSB on it. Cleaned and put back together everything works fine. Word of warning, if you take it apart there is a spring that does,nt play nice. Took awhile to put back together. Be better time spent with new one. Hope this helps somebody.

 

Having had this issue on a 97 once, I can tell you a PO 1870 code is Converter lock up not working. It is one of two things. Either there are excessive internal leaks in the Valve Body & front pump bushing or the converter is burned up.
With all the other codes my guess with over 200,000 miles your looking at a rebuild.
I'm sure a shop will tell you that.
As a former mechanic I can tell you I have seen it more that once changing trans fluid & filter on a trans that maybe in marginal condition & that is enough to end its life. See cleaning it with new fluid takes out a lot of varnish that helped stop internal leaking. The 4L60E is famous for internal leaks. Someone posted a link here once on 4L60E problems that was a big one.
One cheap way to find out if it is internal leaking is drain out a few quarts of fluid & add a couple of quarts of LUCAS STOP LEAK for A/T. If it improves you may get a few more miles out of it. There should be a sticker on these Blazers ADD LUCAS STOP LEAK WITH EVERY CHANGE. Believe me I use it in mine Too Much Stop Leak doesn't compute with these vehicles. Sometime more is better.

 

If you have a steady misfire the ecm will not allow lockup, that being said, I had the same problem before I rebuilt mine. I found when I tore it down the sunshell was almost toast, my 2/4 band was wore out and the 3/4 cluches had seen better days..205,000 miles..