AUTOMATIC TRANSMISSION MODE - Overdrive (D, OD, or a boxed [D])

This mode is used in some transmissions to allow early computer-controlled transmissions to engage the automatic overdrive. 


In these transmissions, Drive (D) locks the automatic overdrive off, but is identical otherwise. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35–45 mph (56–72 km/h).


Under hard acceleration or below 35–45 mph (56–72 km/h), the transmission will automatically downshift.


Vehicles with this option should be driven in this mode unless circumstances require a lower gear.