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.
Check Engine Light With Code P1870 on Chevrolet Express 3500
Average mileage: 98,000 (98,000–98,000)
6 people reported this problem
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Hard 1st and 2nd shift. Starts after the van has been driven for awhile. When van is turned off sand restarted problem is gone.