Check Engine Light With Code P1870 on GMC Safari

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.

RepairPal Verified
Average mileage: 138,000 (126,000–150,000)
Drive Train affected: RWD
7 model years affected: 1995, 1996, 1997, 1998, more1999, 2000, 2002
12 people reported this problem
3 people shared problem details
1997 GMC Safari- RWD150,000
replaced valve body
Check engine light wont go off tune up changed oil
1998 GMC Safari- RWD126,000
code just came on it does it only going over an overpass or normal operating temp.
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