Check Engine Light With Code P1870 on Chevrolet Express 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: 113,000 (51,000–165,000)
6 model years affected: 1996, 1997, 1998, 1999, more2000, 2001
12 people reported this problem
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My van has hard shifts from 1 to 2nd after driving 45min. It more after the transmission temp gets above 190° and then the service engine light comes on with this code. Says sensed a transmission slippage.
Hard shifting between 1 and 2