Intermittent tranny problem

**madramper** · 05-15-2009, 09:21 PM

I have had the suburban for a year or so. It has 172k miles on it. I don't know if the tranny is original or not. Its been fine up until a couple of weeks ago. It started shifting really hard in first and second. It did that for a day and then it was gone. About a week later, it happened again. Again it only happened for a very short time and was gone. Now it seems to be every 3 or 4 days it will happen. It seems that once I shut it off and let it sit, the problem corrects itself. I get a "service engine soon" light and the code is P1870 - Manufacture Controlled Transmission.

Does anyone have any idea what could be causing this? Mechanical or electrical? Also, what tranny is it? It is a 97 GMC suburban with 2wd and a Vortec 350. I believe it is a 4L60E. Is that correct? Are they the same as would be in a car or are they heavier duty for a truck? Sorry, I haven't worked on Chevys very much.

**Bigon37** · 05-23-2009, 01:47 AM

It sounds electrical. Possible that you have a short or lose conection with your shift solnoid. Possible your first gear solniod may have a short that shows up after it gets hot. thats where I would start looking.

**grimreapersshadow** · 05-24-2009, 09:27 PM

good time to do a pan drop and check for metal shavings and such also get some new solenoids from a gm dealer or ac-delco store along with a new filter and fluid fairly simple setup on the 4l60e the solenoids are located at the back and only held in place with a clip unplug and install the new ones there is an ohm test you can perform on em but normaly there way out and just need replacing any way especially with 170K miles on em some parts people might call em a/b solenoids and its the same thing and i recommend using a good quality dex 3 fluid or goin to a full synthetic compadible fluid like royal purple or b&m