1999 GMC Sierra 2500 Problem Reports
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A rattling noise may develop from the AC belt tensioner. This can be caused by an internal fault with the AC compressor, AC performance may also be diminished when this occurs. Our technicians tell us that replacing the ac compressor will commonly correct this concern.
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.