I use it the same as Hawlg. Great for passing too. It's also referenced as the "Sport Mode" switch in the FSM.
Also from the FSM:
When pushing the Overdrive control switch (OD OFF indicator lamp turns ON), the driving condition becomes Overdrive OFF. When pushing again the Overdrive control switch (OD OFF indicator lamp turns OFF), the driving condition changes to D range.
It sounds to me like your switch may be bad, or wires to it have come off.
Remember, you must be in Drive to turn OD off (light on). If you change to Low, the light goes out.
From the owners manual:
Overdrive (O/D) OFF switch When the O/D OFF switch is pushed with the selector lever in the D (Drive) position, the indicator light in the instrument panel illuminates. Use the overdrive off mode when you need improved engine braking. To turn off the overdrive off mode, push the O/D OFF switch again. The indicator light will turn off. Each time the engine is started, or when the selector lever is shifted to any position other than the D (Drive) position, the overdrive off mode will be automatically turned off.
2009 LE AWD Merlot
Loaded w/ NAV 20" rims