What P04FC means
The crankcase ventilation routes blow-by gas into the intake, and CARB requires it to be monitored.
How the engine computer detects it
P04FC is a general function check: pressure or flow in the system deviates from the model. FCA uses it on the 2.0-liter turbo in the Wrangler and Cherokee (2018–19) and the 3.6 Pentastar in the Challenger (2020), with known false triggers fixed by engine module software; the strategy is not published, a FCA patent evaluates a pressure sensor in the fresh-air line.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Possibly oil consumption or oil in the intake
- Whistling from false air
Common causes
- Module software (FCA false trigger) Most likely
- PCV valve or oil separator blocked or sticking Possible
- Ventilation or fresh-air hose leaking or loose, oil filler cap leaking Possible
- Increased blow-by (piston rings) Less likely
How to diagnose P04FC
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: pcv valve, oil separator, crankcase ventilation hose, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 4
- Auxiliary emission controls
- FC
- Specific fault
Questions drivers ask
Can I drive with code P04FC?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P04FC?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P04FC clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.