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 GMC Safari
Average mileage: 138,000 (126,000–150,000)
Drive Train affected: RWD
12 people reported this problem
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replaced valve body
Check engine light wont go off tune up changed oil
code just came on it does it only going over an overpass or normal operating temp.