The overdrive button

Most people believe that when the dashboard lights with an orange light O/D OFF, the car will travel fastest. If you are in this category of people, don't worry, you have actually come to the right site. However I will forgive you for one thing. The overdrive button is actually inverted. We are used to our lighting switch being OFF until we switch it ON. the overdrive button goes contrary to this norm. It is always ON till you switch it OFF.

most automatic cars have a panel against which the gear selector lever slides to aid in selection of appropriate gear. You will see the following numbers and alphabets clearly marked: 1,2,D,N,R,P. I believe from your intuition you understand what 1 and 2 mean. Yes, they mean gear 1 and gear 2. You might wonder, when do you ever need to use this gears in an automatic car. Well here are a few example. Imagine you are going down a steep desent and want to maintain a max speed of lets say 10km/h. Just move the gear selector lever to 1 or 2 depending on the speed you need and you can safely take your foot of the break pedal. The car will maintain a constant low speed down the desent. 

D is the most used in normal everyday driving. It gives the car's automatic transmission system the freedom to do what it was created to do. Except some systems fall asleep on the job and don't know exactly when to do what! Those which stay awake decide what gear to engage at what time depending on the driving conditions.If you are depressing the accelerator pedal slightly, it will most likely be on gear one. It will then move gradually up to gear 2 and 3 as you open the throttle more by depressing the accelerator pedal further down the floor.

N allows you to disengage the engine power from the transmission. But after you do this. you need to make sure you are stepping on the brake pedal or you have engaged the hand brake.It is very unwise to drive on N for an automatic car and I believe any other car. A car in which the engine power transmission to the wheels is cut off will be hard to control under emergency situations. The precision of maneuvers is lost basically for two reasons: One, traction between road and tires is greatly reduced. Two the engine breaking power is non-existent. Only use the N when you are in traffic jam, i.e., when you are physically inside your car. And to make sure this actually happens. You will realize the key will not come out if you switch your car off in N position.

R is self explanatory. This you use to reverse your car. P of course is for parking.

Ok, big question, where is gear 3 and 4? Look at the title of this post again. That is the answer. Actually, the overdrive button is always an ON button. Which means under normal driving conditions overdrive is on. This means the automatic transmission can move all the way from gear 1,2,3 and finally 4. However when you toggle the overdrive button OFF by pressing it, immediately the dash board will light with "O/D OFF". This simply means gear 4 has been cut out of the transmission and the car can only go up to maximum of gear 3.