P04FB on 2020-2025 Cadillac CT4 — Crankcase Ventilation Hose Connection Pressure Sensor Performance
1 vehicles · 1 makes
How to diagnose and fix P04FB: most-reported vehicles
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Cadillac CT4 · 2020–2025
The LSY 2.0L turbo routes crankcase vapors through a PCV/crankcase pressure sensor mounted in the valve cover area. In cold climates and on short-trip driving, water vapor condenses in the sensor port and hose and then freezes, blocking the reference passage. The ECM sees an implausible crankcase pressure signal and sets P04FB (Crankcase Ventilation Hose Connection Sensor Range/Performance), lighting the check engine light. Because the ice thaws once the car sits in a warm shop, dealers frequently find 'no problem found' and simply clear the code, and some replace the sensor unnecessarily. GM addressed it in a preliminary information bulletin covering CT4 and other LSY-equipped vehicles.
Common Symptoms
- Check engine light appears in cold weather
- Code returns after clearing during winter
- No driveability symptom other than the MIL
- Dealer reports 'no problem found'
How to Fix
Per GM's PIP5841-series diagnostic tip, do not replace the sensor on the first occurrence. Remove the crankcase pressure sensor and hose assembly, inspect for frozen moisture or ice, allow it to thaw and drain completely, then clear all residual moisture with low-pressure compressed air and a shop towel before reinstalling. Check the PCV hose routing for low spots that trap condensate. If the code returns repeatedly in warm weather, then diagnose the sensor and the PCV/valve cover assembly itself. Longer drive cycles that fully warm the engine reduce recurrence.
Sources for this issue (2)
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P04FB code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P04FB mean?
P04FB stands for "Crankcase Ventilation Hose Connection Pressure Sensor Performance." The crankcase ventilation pressure sensor is a transducer that outputs a voltage proportional to the gauge pressure between the crankcase ventilation hose and atmosphere; the ECM uses it to monitor PCV system integrity, watching the pressure pulses that track engine airflow and piston motion. P04FB sets when the ECM sees the sensor signal fail to behave as expected — GM's published criterion is the reported pressure remaining outside roughly −0.62 to 0.62 kPa (−0.09 to 0.09 psi) for more than about one second under conditions where a change should be present. In other words the sensor reads a plausible but unchanging or implausible value, so the PCV monitor cannot run.
What are the most common causes of P04FB?
The most common causes of P04FB are: Ice, water or fuel condensate forming in the crankcase ventilation hose or in the sensor port during cold or short-trip operation, blocking the pressure signal, Failed crankcase ventilation pressure sensor, Disconnected, split, collapsed or oil-fouled crankcase ventilation hose, Restricted or blocked PCV passage / oil separator, Open, shorted or corroded sensor wiring or connector. The specific cause varies by vehicle.
How much does it cost to fix P04FB?
Repair costs vary widely depending on the root cause and vehicle.
Which vehicles are affected by P04FB?
Au7o has documented P04FB across 1 vehicle models from 1 manufacturers: Cadillac.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.