1999 Chevy Blazer 4.3:
Man, after fixing the P0753 code by changing the shift solenoids, and changing the trans fluid and filter, I get a P1870 code. It happened 30 minutes after driving it to set the monitors, I did feel it shift hard a couple of times from 1 to 2, but after that it shifts fine. The code didn't set until I was on the freeway, but it seems to be shifting fine, so I don't know what to think.

Here's what I did before that code set: I drove the car for a while before pulling over to check the trans fluid. I checked the trans fluid while in idle, and it was low even though I had put in 5 qts., so I bought some Lucas trans fix and added that in for extra protection. Now, the levels read a bit over, so my question is, could having the trans fluid levels a bit over cause this code? Could the Lucas trans fix have caused this?

 

Reset the code and see if it comes back. There is a lot of info here about the P1870 code so search up if it comes back.

 

Here's an update. I did reset the code, and it never came back. It passed smog with no problems. Thanks!

 

So, if I have P1870 on my 97 Blazer 4.3L and a hard 1-2 when warm, I should replace the valve assy.

Good source for the valve assy anyone?