Check Engine Light With Code P1870 on Chevrolet Silverado 1500

Problem Description and Possible Solution

Vehicles equipped whit a 4 speed automatic transmission may develop a harsh 1-2 shift and/or illumination of the Check Engine Light with code P1870 stored. This can be caused by wear of the bore for the TCC isolator and regulator valves in the valve body. This condition does not commonly occur until the transmission reaches normal operating temperature. If the valve body is worn, replacement will be necessary to correct this concern.

Problem Data
RepairPal Verified
Average mileage: 140,600 (50,000–235,000)
Drive Trains affected: 4WD, Automatic Transmission
3 model years affected: 1999, 2000, 2008
9 people reported this problem
Viewing 1 - 3 of 3 problem details
With the a/c on and the cruise control engaged on a hot day I get the hard 1,2 shifts with the p1870 code.
code 1870 train. slips 1st. to 2nd. not all the time
Check engine light comes on when towing trailer at hwy speeds 70+
Tow haul engaged, transmission in "D"
I had mechanic run the code, which turned up P1870 Transmission slipping