This is a pipe of the crankcase ventilation system. This pipe can redirect the exhaust gas into the intake manifold for combustion.
Automobile engines all have a crankcase forced ventilation system. When the engine is running, some gas will enter the crankcase through the piston ring. If too much gas enters the crankcase, the pressure of the crankcase will increase, which will affect the downward movement of the piston and also affect the sealing performance of the engine. Therefore, it is necessary to exhaust these gases in the crankcase. If these gases are directly discharged into the atmosphere, it will pollute the environment, so engineers invented the crankcase forced ventilation system. The forced ventilation system of the crankcase can re-induct the gas in the crankcase into the intake manifold so that these gases can enter the combustion chamber again. There is also an important component on the crankcase ventilation system, which is called the oil-air separator. Part of the gas entering the crankcase is exhaust gas, and another part is engine oil vapor.
The oil and gas separator separates the exhaust gas from the oil vapor, which can prevent the engine from burning oil. If the oil and gas separator is broken, it will cause the oil vapor to enter the cylinder to participate in the combustion, which will cause the engine to burn the oil and increase the carbon deposit in the combustion chamber. If the engine burns oil for a long time, it may cause damage to the three-way catalytic converter.