If a 1997 Nissan Altima has an amber-colored code O-D OFF on the dashboard to the right of the cruise control what is happening?

If your vehicle has an automatic transmission, look on the shifter for a little button. If you find one somewhere, that button is for Overdrive(O/D).

If you feel more of an engine brake, or notice that the car bogs down when you release the gas pedal, then that is what is happening. look for a button... if you find it, depress it. I hope I was of some help. Good luck.

Added: There is a button on the driver side of the Gear Shifter (near the top). Gear shifter is the lever thatyou use to shift from P(ark) to N(eutral) to D(rive) etc. You can press the button On/Off. This shows up on the dashboard.