Powertrain, generic · Auxiliary emission controls
P04FB Crankcase Ventilation Hose Connection Sensor Range/Performance
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
The crankcase ventilation hose connection sensor is a pressure sensor in the PCV line that measures pressure relative to atmosphere; it is the basis for detecting a disconnected hose (P04DB). P04FB is its plausibility check: GM's 2.0-litre LSY checks the zero point with the engine stopped (at least 10 s, coolant 70 °C or more) – a reading outside ±0.63 kPa or a frozen value sets the code in 128 of 160 samples, MIL after two trips. The disconnection check P04DB is then not possible.
Likely causes
Pressure sensor drifting (zero point error)
Sensor port or line blocked by oil or ice (value frozen)
Contact resistance in supply, ground or signal
Residual crankcase pressure after switch-off (blocked ventilation)
Symptoms
- Check engine light on
- No change in driving
Repair estimate
DifficultyEasyDIY possible
Parts and labour€50–220
Time0.3–1 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
crankcase ventilation hose sensorsensor wiringengine control module
Related codes
References: gsi.ext.gm.com, fordservicecontent.com, law.cornell.edu.