Engine
PCV Valve
The PCV valve vents crankcase gases back into the intake to be burned.
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Combustion flow
Interactive — tap a partTap a part to see how it fits in the system.
What it does
- Draws blow-by gases out of the crankcase
- Prevents pressure buildup and oil leaks
- Burns the gases to reduce emissions
When it fails
- Oil leaks from seals
- Blue smoke on idle
- Rough idle
- Oil in the intake pipes
How to diagnose
- Check the valve rattles when shaken
- Smoke-test the PCV system
- Inspect hoses for collapse
Maintenance
- Replace the PCV valve and hoses on schedule (often every 50,000 km)
- Check for oil in the intake
Use the diagnosis order. When a part fails, confirm each hypothesis with measurements before replacing anything — codes and symptoms overlap.