PCV Valve
What it is
The positive crankcase ventilation (PCV) valve routes blow-by gases from the crankcase back into the intake to be burned, instead of venting them to the atmosphere. It is a small, cheap one-way valve.
What it does
It controls crankcase pressure and recycles blow-by. Stuck open it creates a vacuum leak and a lean condition (P0171/P0174); stuck closed it builds crankcase pressure that can push out oil and blow seals.
Symptoms of failure
- Lean codes P0171 / P0174
- Rough or surging idle
- Oil leaks from seals (stuck closed)
- Whistling vacuum noise (stuck open)
- Increased oil consumption
Common fault codes
Which vehicles need it
Most petrol engines with a traditional PCV valve. A common, cheap contributor to lean codes alongside the MAF.
Replacement cost
| DIY (part only) | $8–$40 |
|---|---|
| At a shop (parts + labor) | $60–$180 |
| Replacement interval | Often every 30,000–50,000 miles (50,000–80,000 km) or at a major service — check your manual. |
| DIY difficulty | Easy (DIY) — usually pulls or unscrews out; one of the cheapest fixes |
| Recommended brands | Standard Motor Products, Fram, OEM, Dorman |
Where to buy the part
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Frequently asked questions
Can a PCV valve cause a P0171 lean code?
Yes. A PCV valve stuck open acts as an unmetered vacuum leak, leaning out the mixture and setting P0171/P0174. It is a cheap part to check before chasing bigger lean-code causes.
How often should I replace the PCV valve?
Many makers suggest every 30,000–50,000 miles or at a major service. It is inexpensive, so replacing it during routine maintenance is good insurance.