Hard shifting problem - error code P1870

I have a 97 Surburban with 156K miles. If I drive for an extended period of time at 70 or higher and then come to a stop, i.e. redlight, I get a very rough almost clunk when the suburban shifts from 1st to 2nd, and then 2nd to third. As long as I"m driving around town, this does not occur. The check engine light comes on and remains on. If I turn the key off, and then right back on, the problem goes away (check engine light stays on). The first mechanic I brought it to said no error codes were found. I brought it to the dealer today and they said it had an error code P1870 and I should replace the tranmision. Another odd thing, is that I recently had the AC compressor replaced. When the aircompressor went bad, the check engine light went off and I did not have any of the above problems. The dealer replaced the compressor and the problems came back (check engine light and hard shifting). Anybody ever see this before? Don't want to put a new transmission in since I have such high miles and not sure how much longer I want to keep it before getting another Suburban. Seems like it might be something computer related as why would turning the car off and then back on, rectify the problem? Thanks in advance.

Here are the main causes for P1870 which is the code for slippage. There was a TSB for 97 GM trucks for this problem and the fix was modifying a ground wire I think. The other cause is the bore for the TCC solenoid gets worn and the the plunger hangs up in the bore preventing the torque converter lockup. The valve body needs to be removed and the bore and plunger repaired. Generally the fix is anywhere from $250-500.00. The other thing I was told that causes this is sometimes one of the checkballs wears through the valve body. In either case until you get it fixed shutting it of and restarting it works sometimes or drive in third. Never drive in 4th when it is acting up or you will overheat the trans. Your other option is to have the whole trans done. I had 176,000 miles on my truck when I got the code so I opted to have the trans rebuilt.

I just bought my Sub a few weeks ago and then this started to happen to mine,the same type of problems. I didn't know what was wrong, and I was worried that it might be very serious. I'll be visiting the dealer soon.

Why does shutting the car off for less than a minute, cuase the probelm to go away? Haven't had a chance to bring it to a transmission shop, but just took a 7 hour trip. No problems until we exited the interstate and came to a stop light. Next stop light, I shut the car off and problem went away and car shifted normally.
Thanks!

Why does shutting the car off for less than a minute, cuase the probelm to go away? Haven't had a chance to bring it to a transmission shop, but just took a 7 hour trip. No problems until we exited the interstate and came to a stop light. Next stop light, I shut the car off and problem went away and car shifted normally.
Thanks!

When the computer senses slippage it will up the pressure in the trans causing the hard shift. When you shut the car off it will reset and even though a code is still logged in the computer it will shift normal until it senses slippage again. Eventually it will get bad enough that shutting it of and restarting won't help. Don't be fooled into thinking nothing is wrong because there is and it will eventually get worse. If you take it in you may find that the bore for the TCC solenoid is worn and may get away with having it modified. The trouble with that is it still cost hundreds of dollars and may only be a band-aid fix or it may go many miles, Either way it is a flip of the coin. While I reccomend you do if you don't get it fixed right away and it keeps acting up make sure you drive in third and not overdrive. With 156k on it I reccomend having it rebuilt.

Hey my wife has a 1999 Suburban 1500 and it did the same thing a couple of months ago. We were exiting the highway and after the light turned green it felt like someone had literally hit us from the back. It happened from the 1-2 shift only though. I thought the tranny was going but once we stopped and restarted for about 5 minutes it quit. Her cousin asked if we used the cruise control on our trip. We did and forgot to turn it off. He said his 1991 Silverado does the same thing sometimes if cruise is left on after coming to a stop. He also said that this is a common problem in Chevy trucks too. Since then we do not use it and it hasn't happened again. It has just turned 100k and I want every trouble mile I can get in the meantime. Hope this helps.