Cause
Blocked oil separator
The separator that removes oil mist from crankcase gases before they return to the intake, restricted so that the crankcase can no longer breathe. It is the part of the ventilation system most often overlooked, because the valve and the hoses are cheap and visible while the separator is usually integrated into the cam cover or the block.
Blocked, it pressurises the crankcase, and pressure finds the weakest seal. Oil is forced past the crankshaft seals, the dipstick tube or the cam cover gasket — so the complaint arrives as an oil leak, and replacing the seal without relieving the pressure means the new one leaks too. A leak that returns quickly after a competent repair is this fault, and it is the single most useful thing to know about it.
It also breaks the intake side. A separator that has failed the other way passes oil mist downstream, which coats the airflow sensor, fouls the throttle body and eventually reaches the intake valves. So one part explains both an external oil leak and a set of intake and metering complaints, and checking crankcase pressure at the oil filler is a quick test that settles it.
Typically a moderate job.
Codes this can cause (4)
Codes where this is a likely explanation first, rather than merely a possible one.
- P04FC Crankcase Ventilation System Performance Likely for this code Moderate
- P051B Crankcase Pressure Sensor A Circuit Range/Performance Likely for this code Moderate
- P04DB Crankcase Ventilation System Disconnected Moderate
- P04FB Crankcase Ventilation Hose Connection Sensor Range/Performance Moderate
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Others who found this
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about Blocked oil separator.