Action Taken When the DTC Sets

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The TCM illuminates the malfunction indicator lamp (MIL).
When in a forward range, the transmission will fail to another forward range, unless the transmission is compromised by over speeding or direction change, then the transmission will shift to NEUTRAL while diagnostic response is active.
If the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, the transmission will shift to NEUTRAL.
If the shift selector is moved to REVERSE, the transmission will shift to REVERSE if it is not compromised by over speeding or a direction change. If compromised, the transmission will shift to NEUTRAL.
DTC P0870 will be stored in TCM history.
The TCM freezes shift adapts (DNA).
The TCM inhibits torque converter clutch (TCC) engagement.