- P - parking (parking brake);
- R - reverse (reverse);
- N - neutral;
- D - forward movement.
So, start the engine, put the lever in position D – and off we go... Until you arrive at your destination and turn off the engine. As you press the gas pedal, the car will automatically start moving, change gears, accelerate, and stop.
Of course, even the smartest automatic transmission can't "guess" what's going to pop into your head a second or two later. It works with a kind of delay: with a manual transmission, you'd have already shifted gears, preparing to overtake, for example, but an automatic transmission will only shift gears the moment you hit the gas and begin overtaking. Therefore, all automatic transmissions have been equipped with additional functions: the position of the selector lever and (if the transmission is electronically controlled) program switch.
Let's consider the purpose and functions of these additional devices using the example of the BMW 750.
P–R–N – it's already clear. The next position is D. In this position of the selector lever, the on-board computer, receiving a signal from the fuel pedal position sensor and from the vehicle speed sensor, changes gears from first (lowest) to fourth (accelerating). There is no engine braking when releasing the gas. But what should you do if it is necessary, for example, on a slippery road or on a descent?
The steps are simple - forcefully engage the gears you need, corresponding to the positions of the selector lever 3-2-1: by releasing the gas and switching the lever to 3, you will feel noticeable engine braking in the range from 100 (should not be used at higher speeds) up to 40 km/h. Then, by shifting into 2nd, you can slow down to 15–20 km/h, and by shifting into 1st, you'll move to a complete stop. It is recommended to practice and learn to brake with the engine on a good, clear road in advance in order to feel the effectiveness of such actions, as they are noticeably different from the "mechanics" we are used to.
The program switch has three positions: S-sport mode, E – economy mode, and M-manual mode. In manual mode, the selector lever position corresponds to the engaged gear. This gives you the ability to operate the transmission as a semi-automatic one. This is convenient when driving on slippery roads, sand, mud, that is, where sudden changes in force on the wheel are unacceptable.
The only difference between the sport mode and the economy mode is that gear changes occur at higher engine speeds.
In cars from other manufacturers, the selector lever may be designed differently, but the functions and control methods are the same. So, on modern American and Japanese cars, after neutral there is a D mode, which means overdrive (OD) and corresponds to the fourth, accelerating gear. Sometimes the selector lever only has forward positions (D, 2 and 1) and an overdrive on/off button (JEEP Grand Cherokee, LINCOLN Mark VIII, etc.). In this case, to turn off fourth gear, you need to turn the button to the "ODoff" position.
It should be noted that on many American FORD cars (Taurus, Escort, Town Car) the selector lever has positions OD, D and 1, meaning it is impossible to force the second gear, which limits the ability to use engine braking and driving on hills.
Owners of cars with automatic transmission must follow several rules:
Check the oil level in the gearbox at least twice a month.
It should be remembered that:
- the oil level is checked only when the engine is running;
- the dipstick usually has marks for both cold and hot oil. If the mark does not indicate the temperature at which the oil level should be checked, do this only on a warmed-up gearbox - after 10-15 km of driving;
- the oil level is usually checked in the parking lot (P). The dipstick is always marked with instructions on how to check it. So, on a JEEP Grand Cherokee, the oil level is checked only in neutral.
Change the gearbox oil after 30,000 km.
It's important to note that Dextron is a universal automatic transmission fluid. The current oil is designated Dextron III. It can be mixed with oils of previous brands (Dextron II, IID, and IIE). It has a more stable viscosity and more powerful additives that improve the operation of the gearbox. CHRYSLER transmissions use MOPAR ATF Plus oil, which can be successfully replaced with Dextron III. ZF transmissions also use Dextron oil, but BMW 540 and 740 vehicles use only ESSO ATF LT 71141 synthetic oil. This oil is also used in all transmissions from this company that bear the green label. Mixing oils is possible if necessary, but not recommended.
Tow a vehicle with an automatic transmission no further than 30 km and at a speed of no more than 50 km/h if the engine is faulty or there is no oil in the transmission.
Remember that if absolutely necessary, you can tow your car over long distances, but you should add an additional 2-3 liters of oil to the gearbox so that all the parts are literally bathed in it.
Avoid overheating the engine, as this can lead to sudden overheating of the oil in the gearbox and, as a result, to failure of the gearbox.
And finally: if you experience noise, vibration, harsh jolts when shifting gears, delayed shifting, etc., immediately contact specialized automatic transmission repair centers, especially if your car has an electronically controlled transmission. Timely diagnostics will prevent significant repair costs.
Don't try to fix the problem yourself – your curiosity, overconfidence, and skimping on DIY projects will cost you dearly.