Is your car hissing with the Check Engine Light on?
Or is your engine misfiring?
These could be bad PCV valve symptoms.
The positive crankcase ventilation valve is essential for your engine as it helps recirculate harmful gasses and reduce emissions.
In this guide, we’ll walk you through the most common symptoms of a bad PCV valve, explain why they occur, and provide tips on how to diagnose these issues correctly.
This Article Contains
- What Does a PCV Valve Do and How Does It Work?
- 6 Bad PCV Valve Symptoms to Look Out For
- How to Diagnose a Bad PCV Valve
- 5 FAQs on the PCV Valve
What Does a PCV Valve Do and How Does It Work?
A PCV valve helps increase fuel economy by redirecting unburned fuel back into the combustion chamber.
Here’s how it works:
As the engine runs, the pistons move up and down inside the crankcase. This movement creates a vacuum pressure that opens the PCV system valve and pulls the crankcase gasses (including oil vapors) into the air intake. The oil vapor then gets mixed with the air-fuel mixture to burn in the combustion chamber, reducing emissions and improving fuel efficiency.
Note that the PCV valve’s behavior changes with the engine’s operating conditions:
- When the engine is idling or running at low RPMs, the increased vacuum in the intake manifold causes the PCV valve to close. This prevents excessive blow-by gasses from being drawn into the combustion chamber during low engine load.
- Conversely, at higher RPMs or during acceleration, the crankcase pressure increases, which causes the spring inside the PCV valve to open. Thus sucking in all excess crankcase gasses and oil vapor into the intake manifold for combustion.
Note: The PCV valve also acts as a safety mechanism. If a backfire occurs inside the intake manifold or crankcase, the car’s PCV valve will close to prevent a potential engine misfire or vacuum leak, respectively.
But what happens if the PCV valves go bad?
Let’s find out.
6 Bad PCV Valve Symptoms to Look Out For
A bad PCV valve can show many signs of failure, including unusual noises, warning lights on the dashboard, and engine misfires.
Let’s take a closer look at how these signs of PCV valve failure manifest:
1. Rough Idle or Engine Misfire
When the PCV valve is stuck or closed, the increased crankcase pressure can disrupt the air-fuel balance in the combustion chamber, resulting in a rough idle as the engine struggles to maintain stable operation. This disruption caused by increased crankcase pressure can also lead to improper combustion and engine misfire. You may also notice rough acceleration at higher RPMs.
Since the valve controls the flow of blow-by crankcase vapors into the intake manifold, its issues may be similar to those of an intake vacuum leak.
2. Noises from the Engine
A malfunctioning PCV valve can cause the engine to produce a whistling or hissing sound. This happens when the valve has a slight blockage and is stuck open.
Although the noises eventually disappear as you continue driving, it’s always best to get it checked out. Ignoring it can lead to further engine damage.
3. Blue Exhaust Gas Emission
If the positive crankcase ventilation valve is stuck open, you may notice blue smoke from the exhaust pipe. That’s because a stuck valve forces excess engine oil vapors to mix with fuel and crankcase gasses during combustion. This causes the engine to burn the air-fuel mixture along with engine oil. Hence, the exhaust pipe releases blue smoke.
Sometimes, the exhaust gas emission can also appear white or black instead of blue.
4. Illuminated Check Engine Light
A clogged PCV valve can cause the Engine Control Unit (ECU) to trigger the Check Engine Light and produce a DTC code.
Some common trouble codes often associated with a faulty PCV valve include:
- P052E: Positive Crankcase Ventilation Regulator Valve Performance
- P053A: Positive Crankcase Ventilation Heater Control Circuit/Open
- P0171: Fuel System Too Lean
- P0300: Random/Multiple Cylinder Misfire Detected
5. Oil Leaks
When the PCV valve is stuck closed, the blow-by gasses and oil vapor accumulate, resulting in excessive crankcase pressure buildup. This could lead to oil seeping out of the PCV system seals and valve cover.
So, if you see puddles of oil underneath the car and there isn’t any damage to the oil system, you can safely assume that the oil leak stems from the PCV system or valve cover. If the oil leak is left unattended, you could have fouled spark plugs and excessive oil consumption.
Note: The excessive crankcase pressure from a faulty PCV valve can create a strong suction on the oil cap or leave a film-like residue on its underside. If your PCV valve is clogged, harmful gasses can accumulate in the crankcase oil, leading to sludge formation inside the engine.
6. Poor Engine Performance
If your car’s PCV valve is stuck open or closed, it can throw off the air-fuel mixture ratio in the combustion chamber, leading to irregular engine operation, a drop in fuel efficiency, and increased engine emissions.
Now you know the warning signs of a failing PCV valve.
But how can you be sure these bad PCV valve symptoms are due to the valve itself and not some other problem?
Read along to know how.
How to Diagnose a Bad PCV Valve
Here’s how an auto repair mechanic will diagnose a PCV valve for damage:
- First, they’ll inspect the PCV valve grommets for cracks or splits. Since they’re made of rubber, these grommets can crack if exposed to engine heat for long, allowing dirt and dust to enter the valve.
- If the grommets are fine, they’ll check the PCV valve hose for swelling or cracks. The vacuum hose can degrade and harden over time and eventually form cracks, giving way to a vacuum leak. They’d also look at the valve cover to ensure it’s in top condition and isn’t oil-soaked.
- Next, the mechanic will inspect the PCV valve body. They’ll remove the valve from the cover grommet and disconnect the PCV valve hose. Testing the valve is pretty straightforward—they’ll shake it and listen for any rattling noises.
- If the PCV valve functions correctly, it’ll produce a rattling sound when shaken.
- However, a faulty PCV valve wouldn’t produce any sound, indicating that something is causing the valve to get stuck, and they’ll have to clean it.
- If the PCV valve functions correctly, it’ll produce a rattling sound when shaken.
- The mechanic will also check the airflow through the PCV valve to ensure proper operation. To test the airflow, they’ll reconnect the valve to the vacuum hose, start the engine, and let it idle for 15 minutes.
Once warm, they’ll disconnect the valve from the valve cover and cover its end with their finger.- If they feel suction and the idle slightly drops, the valve is functioning properly.
- If there’s no suction or a significant drop in engine revs, the PCV valve needs replacing.
- Finally, the mechanic will observe the inner lining of the PCV valve for any signs of moisture contamination — a cloudy or milky film inside the valve or its vacuum hose. If the PCV valve is contaminated, they’ll need to replace it and perform an oil change.
Why?
That’s because moisture typically enters the system if there’s oil contamination.
Still have more questions about the PCV valve?
Check out these FAQs to get your answers.
5 FAQs on the PCV Valve
Here are the answers to five common questions on the PCV valve:
1. Can You Drive With a Malfunctioning PCV Valve?
No. Driving with a failing PCV valve isn’t advisable, regardless of whether you drive a Honda Motor Company car, a Ford, or a Mini Cooper.
While driving short distances may be possible, long-distance driving can severely damage your engine. It can lead to problems like rough acceleration, blown gaskets, and excessive oil consumption (due to severe oil leaks), resulting in costly engine repair.
2. Can You Clean the PCV Valve?
Yes, but it isn’t recommended.
Though cleaning a clogged PCV valve with WD-40, a brake cleaner, or an electrical contact cleaner will work temporarily, it’s always better to get a PCV valve replacement. Also, sometimes, the valve may appear clean, but the springs inside might be too old and worn out for you to notice.
3. How Long Does the PCV Valve Last?
Most manufacturers suggest replacing the PCV valve every 20,000 miles to 50,000 miles. However, this range may vary depending on your driving habits.
If you drive short distances every time, there’s a chance that you’ll encounter a PCV valve failure earlier due to excessive moisture buildup than if you constantly drive long distances.
4. How Much Does PCV Valve Replacement Cost?
The cost of replacing a bad PCV valve ranges from $185 to $220.
But, these costs can vary based on your vehicle’s make and model, whether you get original or aftermarket parts, and labor rates at your local repair shop. Typically, a professional mechanic will need about 1 to 2 hours to diagnose and replace a PCV valve.
5. How to Maintain and Prolong the Life of Your PCV Valve?
To extend the life of your PCV valve, it’s recommended that you keep up with your car’s oil change and air filter replacement schedule. Old engine oil can accumulate dirt and sludge, leading to potential buildup on the valve. On the other hand, increased crankcase pressure due to a clogged air filter can damage the valve and lead to expensive engine repair.
Replace Bad PCV Valves with AutoNation Mobile Service
Signs like an illuminated engine light, excessive oil consumption, or poor fuel economy could be due to a malfunctioning PCV valve.
If you notice these signs, it’s best to play it safe and have your car inspected by a professional — like AutoNation Mobile Service — to avoid severe engine damage.
We’re a mobile auto repair and maintenance solution offering easy online booking and a 12-month| 12,000-mile warranty on all car repair services.
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