I just wanted to let you guys know something interesting that I came across the other day. I was driving my new 99 blazer around and the dreaded p1870 code came up and after a while it started shifting hard as hell. I read all about this and was thinking I was going to have to get the valve body worked on. However I just got this truck and thought there was something funky with the brakes. So I went looking around underneath and took off the rear wheels to find that the new brakes the guy put in the back were completely gone on one side. I decided to look at the other side; they weren’t even touched to speak of. Well I found that that caliper was completely stuck and the other side would go out and not retract properly. So I replaced them and then drove the truck around, long distances < 30 minutes. Code went away, no more hard-shifting. However the transmission fluid looked like crap (It had never been done) so I got it flushed the other day. It is still doing well, with no problems so far. So one stupid caliper being locked up was making the truck shift more than it had to and made it think something was slipping, I guess. If anyone else gets this code I know it won’t help many, but maybe someone will experience the same thing.

 

That condition will not cause the P1870 code to trigger. It could have been a fluke, but I'm betting that sooner or later the code will return.

 

I just was saying that before it happened in a 20 mile trip, after I went on a ~150 mile trip and it didn't happen. (before the tranny fluid change) Before it was shifting a lot to keep at a constant speed now it isn't.