1. Taking precautions, pull over to the side of the road or to the edge of the roadway and stop.
2. Move the range selector lever to the "P" (parking) position (cars with automatic transmission) or shift the gear lever to neutral (cars with manual transmission). Set the parking brake
3. Turn off the air conditioner.
4. Check for coolant splashes or steam coming from under the hood or from the engine compartment.
If steam is coming out of the engine compartment
Do not go too close to the front of the vehicle. Turn off the engine. Then turn the ignition switch to the "ON" position (ignition on). Do not start the engine. The cooling fans will turn on and begin to cool the engine.
In the absence of steam release and coolant discharge
Open the hood and let the engine idle until it cools down. If the engine temperature does not drop, turn off the engine and let it cool down.
5. After the engine has cooled down, check the coolant level. If the coolant level is below normal, check for leaks in the radiator connections and hoses, heater heat exchanger, radiator, and in the coolant pump seals.
If you have not found any faults and there is no coolant leak, then after the engine has cooled down, carefully add coolant and bring its level to normal.