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What Is a PCV Valve and How Does It Work?

What Is a PCV Valve and How Does It Work?

18th Nov 2021

Positive crankcase ventilation (PCV) valves are commonly found in cars, trucks and SUVs. Assuming your vehicle has a combustion engine -- as opposed to an all-electric engine -- it will likely feature a PCV valve. Like with many other types of valves, it's designed to control the direction in which gases travel. What is a PCV valve exactly, and how does it work?

Overview of PCV Valves

A PCV valve is a small valve that's found inside the crankcase of combustion engines. It's used to route combustion gases from the crankcase back into the combustion chamber. As your vehicle's engine burns a mixture of gas and air, it will create combustion gases as a byproduct. Rather than releasing these exhaust gases into the atmosphere, a PCV valve will recycle them. It will send the combustion gases back into the combustion chamber.

How PCV Valves Work

While there are different types of PCV valves, they all work in the same way. PCV valves allow combustion gases to pass through them from one direction, but they prohibit combustion gases from passing through them from the opposite direction. In other words, they are one-way valves that force combustion gases to travel in a single direction.

Signs of a Bad PCV Valve

A bad PCV valve can manifest in several ways. Oil sludge, for instance, is a common symptom of a bad PCV valve. When your vehicle's PCV valve fails, combustion gases may mix with oil inside of the crankcase. Over time, this can lead to oil sludge with a thick and heavy consistency.

Poor fuel economy is another common symptom of a bad PCV valve. Fuel economy is determined by how efficiently your vehicle can burn gas and air to create combustion. A functional PCV valve will improve your vehicle's fuel economy by recycling its combustion gases, meaning it won't have to burn as much gas to create combustion. If it fails, on the other hand, you may experience poorer fuel economy when driving.

The Check Engine Light (CEL) may turn on if your vehicle has a bad PCV valve. CELs can trigger for any number of reasons. If your vehicle's computer detects a problem with the engine, it will likely trigger the CEL. A bad PCV valve may cause the CEL to turn on. You can use a code reader to investigate what causes the CEL to turn on. If a bad PCV valve is to blame, you'll need to replace it.