How do I know if my Subaru PCV valve is bad?
Common signs that your Subaru's PCV valve may be failing include a rough idle, oil leaks or burning oil smell, higher oil consumption, and sometimes a check engine light. A quick shake test and hose inspection can help you decide if it's time to replace. Replacement is relatively inexpensive and can prevent crankcase and intake problems from developing.
Key signs of a failing PCV valve
The following symptoms are the most commonly reported indicators that the PCV valve is clogged or stuck, which can disrupt crankcase ventilation and engine vacuum.
- Rough idle or stalling at idle
- Fluctuating idle or unexpectedly high idle RPM
- Check engine light or codes related to vacuum/air-fuel mixture (codes like P0171/P0174 can appear on Subarus, though codes vary by model)
- Oil leaks around the valve cover or intake hoses, or a noticeable oil smell in the engine bay
- Oil buildup or sludge in the PCV hose or valve, sometimes with oil in the intake
- Increased oil consumption or smoky exhaust due to oil being vented improperly
- Cracked, hard, or oil-soaked vacuum hoses linked to the PCV system
If you notice several of these signs, inspect the PCV valve and its hoses and consider replacement to prevent further engine issues.
How to test the PCV valve
Use these steps to determine whether the PCV valve is functioning or needs replacement. If you're unsure or uncomfortable with DIY checks, consult a mechanic.
- Locate the PCV valve and its vacuum hose connected to the valve cover and intake manifold. On many Subarus, it sits on or near the valve cover with a rubber hose leading to the intake.
- With the engine off, remove the PCV valve and shake it. A healthy valve typically rattles or slides smoothly; if there is no rattle or it moves with excessive resistance, replace it.
- Reinstall the valve and start the engine. With the engine idling, lightly pinch the PCV hose near the valve to feel for suction. There should be noticeable vacuum; little or no suction can indicate a clogged valve or hose.
- Inspect the attached hoses for cracks, stiffness, or oil saturation. Replace any damaged or oil-soaked hoses.
- Reinstall a new or cleaned PCV valve and take the car for a test drive to confirm that idle smooths and symptoms resolve. If problems persist, further vacuum or intake issues may be present.
These checks help distinguish a bad PCV valve from other vacuum or intake problems. If the valve rattles and there is proper suction in the hose, the valve is likely functioning; if not, replacement is warranted.
Replacement and maintenance
If tests indicate a faulty PCV valve, follow these steps to replace it and maintain the system to prevent future issues.
- Purchase the correct PCV valve for your Subaru model/year (OEM or a reputable aftermarket equivalent).
- Remove the old PCV valve and inspect the connecting hose for wear or oil saturation; replace the hose if it’s cracked or contaminated.
- Install the new PCV valve with the hose connected securely and clamps tightened to specifications.
- Reconnect all hoses, start the engine, and check for leaks or abnormal vacuum behavior. Take a short test drive and monitor for improvements in idle and performance.
- Dispose of the old valve properly and keep an eye on oil consumption or new codes over the next few weeks; address any recurring issues promptly.
After replacement, recheck idle and vacuum and monitor for oil leaks or codes. Regular inspection of PCV hoses and connections helps prevent future failures and keeps the system venting crankcase gases effectively.
Summary
In short, a bad PCV valve in a Subaru often shows up as rough or unstable idle, oil leaks or burning oil smells, and, sometimes, an illuminated check engine light. A simple shake test, plus hose inspection and vacuum checks, can help you identify a faulty valve. Replacement is inexpensive and straightforward, and pairing a new valve with any worn hoses typically resolves symptoms and protects the engine from sludge buildup and crankcase pressure. For best results, consult your owner's manual for maintenance intervals and consider professional service if you’re unsure about diagnosis or replacement.
