I keep getting a P1870 code in my 99 Sierra. The tranny works perfect and doesn't slip at all. When it throws the code and bumps up line pressure the 1 2 shift is very hard until I clear the code and it goes back to running perfect again. Any idea why I keep getting a slipping code if it isn't actually slipping?

 

It might be an issue with the TCC operation in the valve body. There are a few different ways to correct this if in fact it is your issue. My suggestion would be to remove the trans pan and do a visual inspection of the pan. If it does not look good you need to start planning on a new trans. If it looks pretty good you could install a Trans-go kit and this will address the issues with the regulator valve that wears the bore in the valve body. There is a cheap fix for this as well. Depending on which factory valves are in your valve body for this line up you can pin these valves and it will help. In some cases a longer spring can be used between the two valves in the early valves.

The spring of choice in the industry seems to be an inner pump priming spring from pump slide area. I have even seen one of the sponsors here use check ***** to do this. With one of the line ups you can actually just flip the inner most valve and reinstall the spring, out board valve, end plug and the retaining clip. By doing these mods the LU will be firmer but it does correct the 1870 code if this part of the trans is what is causing it. I will recommend if you are going to do this to make sure that you get a new separator plate and replace it while you are in there. In some cases you will find that the check ***** have damaged the plate so you might as well replace it while your in there. HTH Vince

 

I assume thats the issue. I took the pan off the other night and it was quite clean. http://www.transgo.com/A1_4L60E-4L65E.html is this the kit you're talking about? My tranny is doing exactly what that kit says it fixes.

 

Yes thats the kit I was talking about.

 

Did you get the kit? Did it help?

I'm in a similar situation and am considering doing the same kit and maybe servos, cooler, and a deeper pan to see if I can get another 100k miles out of it.