RAM 1500 Owner's Manual page 427

Electronic Range Select (ERS) Operation
The Electronic Range Select (ERS) shift control allows the
driver to limit the highest available gear when the shift
lever is in the DRIVE position. For example, if you shift
the transmission into 3 (third gear), the transmission will
never shift above third gear, but will shift down into
second and first gear normally.
You can switch between DRIVE and ERS mode at any
vehicle speed. When the shift lever is in the DRIVE
position, the transmission will operate automatically,
shifting between all available gears. Tapping the ERS (-)
switch will activate ERS mode, display the current gear in
the instrument cluster, and maintain that gear as the top
available gear. Once in ERS mode, tapping ERS (-) or (+)
will change the top available gear.
Column Shift Lever
To exit ERS mode, simply press and hold the ERS (+)
switch until "D" is once again displayed in the shift lever
position indicator in the instrument cluster.
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