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GMC Sierra 2500 Problems

Check Engine Light With Code P1870 on GMC Sierra 2500

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.

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GMC Sierra 2500 Vehicles With This Problem

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Average mileage: (–)
2 model years affected: 1999, 2000
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