What Happens If PCV Valve Is Disconnected

I felt that my engine performance had been running weak for many days, and that turned out to be a big disaster when I was going on a trip, and I heard multiple engine misfires, resulting in increased exhaust emissions. I had to stop the Jeep, check the problem, and discover that my vehicle’s PCV valve was disconnected. I didn’t understand what to do there because I didn’t know what would happen if the PCV valve was disconnected. I was worried and wanted to see the solution; therefore, I collected information to solve the problem. In this article, I will share all the information about what happens if the PCV valve is disconnected.

What Is A PCV Valve And How Does It Work?

Before we start to know about disconnected PCV valves, it is important to learn what a PCV valve is and how it works. It is commonly known as a Positive Crankcase Ventilation PCV valve. It is a tapered cylindrical metal or plastic centerpiece that is present on the outer housing with holes at the top and bottom and is held in place with the tension spring. It is responsible for properly working an efficient engine by redirecting unwanted and harmful gases in its combustion process. Its purpose is to protect your vehicle crankcase, the engine, oil, and the environment. 

Why Does PCV Valve Disconnected?

When it comes to reasons, there are several things that make the PCV valve disconnected. Some are mentioned here.

  • Aging: With time and excessive use of PCV valves, the system, like valves, hoses, and fittings, becomes brittle, deteriorate, or corrode. 
  • Improper PCV Installation: If you have recently installed a new one or repaired the previous one, the disconnection occurs due to improper installation. 
  • Vibration and Engine Movement: The PCV system continuously functions when your vehicle engine is on. As the car moves, the vibration occurs, and all these things make the PCV system connections loose, making the valve disconnect.
  • Physical Damage or Blockages: Any physical damage or blockage due to a clog in the system causes disconnection. 
  • Accidental Damage: While servicing, engine repair, or maintenance, the PCV valve may be accidentally disconnected or even, due to mechanical negligence, left unattached. 
  • Excessive Pressure: If there is a clog in an air filter or an oil separator, malfunctioning causes high-pressure levels on the engine, which forces the PCV valve to disconnect.
  • Material: If you have to install a new PCV valve or repair it, remember to check the material, as incorrect parts and poor material lead to disconnections.
  • Environmental Factors: The heat the vehicle produces or the extreme temperatures or environmental conditions affect the PCV system and weaken it, further leading to disconnection.
  • Tampering: Another reason is the driver, as people intentionally disconnect the valve while thinking that it enhances engine performance.

How Does PCV Valve Suddenly Disconnected?

There are several factors and a combination of events that cause the PCV valve to disconnect suddenly. For your proper understanding, I have discussed the whole process of how this disconnection might happen:

  • Constant exposure to heat, engine vibrations, and chemical reactions occur due to engine gas combustion weakens the PCV valve and the hoses associated with it. All these things develop small cracks on the PCV, make it brittle, and even cause it to lose its elasticity. 
  • All these conditions increase the load on the engine through rapid acceleration or high-speed driving. With this increase in loads, high pressure is generated in the crankcase. 
  • This pressure goes from the crankcase to the PCV system, which includes the PCV valve and its associated hoses. 
  • When this pressure comes to hoses and valves, they can’t withstand it because of their poor, weakened, or deteriorated condition. 
  • This pressure forces one end of the hose or the PCV valve itself to disconnect from its fittings or ports.
  • Once the hose or PCV valve disconnects, the PCV system is no longer able to continue its normal functioning. 

Disconnected or Defective PCV Valve Effects

Disconnected or bad PVC Valve causes many problems to the engine and sometimes, in extreme cases, causes engine damage. A faulty PCV fails to vent exhaust gases in the engine, and these harmful gases build up pressure inside the engine, causing major oil leaks and other problems. It will minimize the amount of air entering the engine, reduce fuel efficiency, and cause rough idle problems.

What Happens If PCV Valve Is Disconnected

What Happens If PCV Valve Is Disconnected

Removing the PCV valve or disconnecting the PCV valve or tubes connected to it can cause some severe issues to your car engine and the environment. Some important critical and prominent impacts are as follows:

  • Oil Contamination 
  • Sludge and dirt buildup
  • Oil leaks
  • High fuel consumption
  • Engine misfires
  • Hard engine starting
  • Rough idle
  • black smoke
  • Spark plugs fouled with oil

It will increase oil contamination and check engine light, which is a warning light and may also light up. Sometimes, error codes also indicate malfunctioning of the mass airflow and oxygen sensor, making it difficult for users to diagnose the problem. 

The crankcase holds motor oil at the bottom of the engine. When gasoline is burnt in your engine and creates waste gases, it will be released through the exhaust system. PCV valve is where some gases manage to get past the piston; if PCV gets disconnected, gases combine with motor oil and create sludge. It will automatically harm the engine components and block the engine channels. 

Blow-by gasses escape from your vehicle’s engine and are recycled to its crankcase through PCV. These gasses in the combustion chambers again burnt after recirculation. PCV’s function is to prevent the accumulation of such gases; if it doesn’t do it, the gasses cause an accumulation of sludge in the oil of the engine after condensation. 

If you have this question about what happens if PCV Valve is disconnected, the answer is simple: the gasses in the engine accumulate, entering the engine’s oil and thus causing the issues in your vehicle. Moreover, disconnecting the PCV valve isn’t entirely detrimental, as it allows the combustion process to access cleaner air.

How Can I Fix My PCV Disconnected Valve?

Fixing the disconnected PCV valve is easy, but we recommend not doing the process yourself if you don’t know the vehicle’s mechanics. Let’s see the fixing guide.

  • Make sure to park your car in a parking lot or some safe place with a flat and stable surface. Remove the ignition key, turn off the engine, and let it cool down. 
  • If you know where the PCV valve is, then it is good; otherwise, check your Jeep service manual to know the exact location. However, mostly, it is located on or near the engine’s valve cover or intake manifold.
  • Find the reason for disconnection, and check if something is damaged or worn out. If a hose is disconnected, you have to reattach it to the PCV valve and the intake manifold or air intake system.
  • Find if there are any cracks in the system or blockages or clogs in the valve. Remove the blockage or replace the valve In case of damage.
  • In case of damaged hoses or the PCV valve, you have no other choice than to replace the damaged parts immediately. 
  • If you want to install a new PCV valve, just disconnect the previous one from the hose and unscrew it from its mounting location. Install a new one, connect it with a hose, and screw it in the exact location. 
  • If hoses are not attached securely, then attach them, or you can use hose clamps or clips to prevent future disconnections.
  • Testing is necessary, so start your Jeep’s engine and check if the system starts functioning or working correctly. Check if you hear any unusual noises or air leaks. 
  • If disconnection causes an engine fault code, you can use the OBD-II scanner to remove the error from your Jeep’s computer. 
  • Regular maintenance is also essential, so keep it in mind to regularly check your PCV system and engine functioning. 

What happens if the PCV Valve is damaged?

We have already discussed what happens if the PCV valve is disconnected. Now, we find out what happens if the PCV valve is damaged. It will most commonly affect your vehicle engine as it may experience several issues. The most prominent ones are lower power output, decreased fuel efficiency, and higher emissions. A Malfunctioning PCV valve also turns the engine light on, and different issues related to the engine. As the engine is the vehicle’s major part, choose skilled auto repairs to fix the PCV valve failure problem. It needs to be immediately repaired, cleaned, or replaced to continue the engine’s proper functioning. 

What Is The Reasons To Replace The PCV

Disconnected the PCV valve exposes the engine to moisture and harmful debris, and it also stops the exhaust gases from escaping the engine and restricts the airflow to the engine, causing the engine performance to slow down and increase fuel consumption. So, whenever you see bad PCV valve symptoms, it is necessary to maintain and take care of a faulty PCV valve, and if it is in worse condition, choose an expert auto mechanic to repair or replace it. 

How To: Diagnose and Replace a PCV Valve


What if the PCV valve becomes jammed open?

If the PCV valve becomes jammed open, it pushes oil through the engine’s seals and gaskets. If your vehicle has a leaky hose or a stuck open PCV valve, it will cause many issues like vacuum leaks, difficulty in driving, and rough idle. In case of a corroded or closed vehicle PCV valve, the engine oil will return to the breather and cause the abovementioned issues.

Is it possible to drive a car without the PCV valve?

It can, but you mustn’t. The valve is connected to your car’s intake manifolds with the help of rubber hoses. If your vehicle has no PCV or you have removed it, the hose will no longer connect to the engine, resulting in a big air leak, further leading to rough or dying the engine.  


We have discussed in detail here what happens if the PCV valve is disconnected. Though PCV is a small piece of your vehicle, it performs the significant function of saving the engine from damage by redirecting unwanted and harmful gases in its combustion process and making it function properly and efficiently. So, don’t think of making it disconnected manually, and in case it does automatically due to any reason, find the issue and solve it. 

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