Crankcase Breather Hose
Carries blow-by gas from the crankcase back to the intake so it can be burned rather than vented. Venting it to atmosphere has been illegal for decades, which is why modern engines actively detect a hose that has come off — some carry a connection sensor whose only job is to answer whether it is plugged in.
A detached or split hose does three things at once, and they are usually reported as separate complaints: it releases oil vapour to atmosphere; it admits unmetered air to the intake, so the mixture goes lean and fuel trim codes follow; and it stops the crankcase being evacuated, so pressure rises and pushes oil past the crankshaft seals. That last one is how a hose failure becomes a seal replacement.
They go brittle with heat and age and fail out of sight — splitting along their length or snapping at an elbow, often underneath the intake manifold — and a split reads identically to a disconnection on any sensor that only checks the connector. So the hose is inspected physically, not by code.
A hose that popped off was pushed off. Look for a blocked separator or a stuck PCV valve behind it, or it will come off again.
Also known as: breather hose, crankcase vent hose, pcv hose, blow-by hose, oil separator hose
Referenced by 13 codes
Codes involving this component (13)
- P04DB Crankcase Ventilation System Disconnected Moderate
- P04E2 Crankcase Ventilation Hose Connection Sensor Circuit Low Moderate
- P04FB Crankcase Ventilation Hose Connection Sensor Range/Performance Moderate
- P04FC Crankcase Ventilation System Performance Moderate
- P051B Crankcase Pressure Sensor A Circuit Range/Performance Moderate
- P04E1 Crankcase Ventilation Hose Connection Sensor Circuit
- P04E3 Crankcase Ventilation Hose Connection Sensor Circuit High
- P04E4 Crankcase Ventilation Hose Connection Sensor Circuit Intermittent/Erratic
- P051F PCV Filter Restriction
- P053A PCV Heater A Control Circuit /Open
- P053B PCV Heater A Control Circuit Low
- P053C PCV Heater A Control Circuit High
- P053D PCV Heater A Performance
Other components in Air Intake and Metering
- Intake Air Temperature Sensor 83
- Throttle Body 69
- Throttle Position Sensor 58
- Intake Manifold Tuning Valve 56
- Mass Air Flow Sensor 52
- Intake Manifold 51
- EGR Throttle Valve 38
- Throttle Actuator Motor 34
- PCV Valve 31
- Air Filter 30
- Manifold Absolute Pressure Sensor 29
- Crankcase Pressure Sensor 14
- Intake Air Heater 11
- Idle Air Control Valve 9
- Intake Air Oxygen Sensor 7
- Humidity Sensor 5
- Air Cleaner Inlet Actuator 3
Information, not instruction
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