Humidity Sensor
Measures water vapour in the intake air, which most drivers would not guess an engine cares about. It does, for a reason worth knowing: water vapour displaces oxygen and absorbs heat during combustion, so it lowers peak flame temperature.
That gives the module two things. Nitrogen oxide formation falls as humidity rises, because NOx is made by heat — so an engine that knows the humidity can trim exhaust gas recirculation precisely instead of assuming a worst case. And knock margin improves for the same reason, so a petrol engine can safely run a little more ignition advance on a humid day.
Which makes a wrong reading a quiet efficiency loss rather than a breakdown. The engine falls back to conservative assumptions and gives up a little economy and power, with nothing a driver would feel.
It is usually built into the intake air temperature or mass airflow assembly, so a fault here often means that whole unit — and if the temperature channel is also implausible, the assembly or its connector is at fault rather than the humidity element. Contamination is its characteristic failure: oil mist from a leaking breather or an over-oiled aftermarket filter poisons the element, and a replacement fitted behind the same filter fails the same way.
Also known as: intake humidity sensor, air humidity sensor, relative humidity sensor, moisture sensor
Referenced by 5 codes
Codes involving this component (5)
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
- Crankcase Breather Hose 13
- Intake Air Heater 11
- Idle Air Control Valve 9
- Intake Air Oxygen Sensor 7
- Air Cleaner Inlet Actuator 3
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