P04FB on Cadillac
Crankcase Ventilation Hose Connection Pressure Sensor Performance
P04FB on Cadillac vehicles indicates crankcase ventilation hose connection pressure sensor performance. Au7o has documented this code across 1 Cadillac model — most commonly on CT4. 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.
Common Causes of P04FB
- •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
P04FB on Cadillac by Model
Cadillac CT4(1 issue)
- Crankcase Pressure Sensor Ices Over in Cold Weather Setting P04FB2020-2025
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.
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View P04FB across all makes →Frequently Asked Questions
What does P04FB mean on Cadillac?▼
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. On Cadillac specifically, this code is documented across 1 model.
What causes P04FB on Cadillac vehicles?▼
Common causes on Cadillac: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P04FB on a Cadillac?▼
Repair costs vary widely depending on the root cause and specific Cadillac model.
Which Cadillac models have P04FB documented?▼
Au7o has documented P04FB on 1 Cadillac model: CT4.