P1870 is common. There is a valve that wears the body and will start to stick. It will be most noticeable during the 1-2 upshift as the computer will have to increase the pressure to work
the sticking valve. If you haven't had the code long enough for the sticking valve to wear out the clutches you can but a tool to fix the valve body and replace the valve.
The problem really is the lockup coverter. The trany is taking too long to lock or unlock the convertor. When the computer detects this has occured twice in a row, it goe into OS mode. It decides it's slipping so it turns it's pressure up to the max. You get kicked in the A everytime if shifts from 1st to 2nd?
When is the last time you checked the fluid? Make sure it is correct color and amount... then look into THIS THREAD
to find an aftermaket fix for your problem. (Trans Go Kit)
Comment posted on Jul 21, 2009
This comment in particular:
No, if the CEL is on and if it's a 1870 code.
Typical it will be OK when it's cold. It takes a lot of stop and go, or a little freeway to bring it up to failure temp. So every day things start off OK, but the shifts are a little off. If I was driving on the freeway at about 50 then slowed down and speed back up it would do something strange. It seemed to slip or shift gears slightly back and forth. Anyway after it's warm it starts to shift hard from 1st to 2nd even at light trottle. The problem is the lockup coverter. The trany is taking too long to lock or unlock the convertor. When the computor detects this has occured twice in a row, it goe into OS mode. It desides it's slipping so it turns it's pressure up to the max. You get kicked in the A everytime if shifts from 1st to 2nd.
Why this occures is on of GM's trans improvements. On the older version of this trans. (and those with the shift kit installed) you will feel it when the convetor locks and unlocks. Some ******** at GM desided this is a bad thing. His fix is insted of just locking and unlocking, he came up with a PWM system that would slowly lock and unlock by slipping the clutch in the convertor. To do this the PWM valve in the valve body bounces back and forth rapidly as the clutch locks or releases, as oposed to just moving once from lock to unlock. Guess what this does? It wares out part of the valve body! Are you getting the big picture
yet! GM fixes this by replacing the valve body. The new ones don't have this failure mode (so says GM). The Trans Go kit make all of the shifts short and sharp, you will feel it every time the convertor locks or unlocks. It occures just above 40MPH at light throttle.
Hell, I could have told him that would happen! As part of the kit you will modify the servo and add springs. I do not think you will need a Vet servo after the kit is installed. If you do your homework first, you might get the job done in 5 hours. It took me longer, I did not know how to remove the servo.
Good luck. Also if your fluid is burnt, you will need a rebuild. The seals and clutches will be fried.
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