What does it mean?
The module feeds the humidity sensor a reference voltage and reads back a signal voltage that represents relative humidity. This code is stored when that signal sits below the lowest voltage a working sensor is able to produce, typically a few tenths of a volt, and stays there longer than the calibrated time. A value that low is not a real humidity reading, so the module treats it as a circuit fault rather than a measurement to be used. In practice it points to the signal wire touching ground, a shorted sensor element, or a lost reference feed that leaves the input sitting at zero.
Symptoms
- MIL on with the humidity reading pinned at or near zero
- Softer acceleration as the module applies conservative spark and boost management
- On diesels, EGR and NOx strategy running on a substitute value with more visible smoke
- Small increase in fuel use
- Rough running that is more noticeable in cold, damp conditions
- The fault returning immediately after a code clear if the short is permanent
Likely causes
- Signal wire shorted to ground through chafed insulation or a pinched section of harness
- Internal short inside the sensing element
- Missing reference voltage, which collapses the signal to near zero regardless of sensor condition
- Water or coolant residue in the connector bridging the signal and ground terminals
- Terminals bent or pushed together inside the connector housing
- Harness damaged where it passes a bracket, clip or duct edge under tension
- Rarely, a shorted input circuit inside the control module
How to fix it
- Note the freeze frame and confirm the low signal is present live rather than only historic
- Unplug the sensor with the key on and read the signal terminal; if the voltage rises toward reference the sensor is shorted, if it stays low the harness is
- Check for correct reference voltage at the connector, since a missing reference imitates a shorted signal
- With the module connector disconnected, measure resistance from the signal wire to ground to locate a short
- Inspect the connector for moisture, corrosion and terminals that have been pushed in or bridged
- Repair the shorted harness section, secure it away from edges and heat sources, then retest
- Replace the sensor if it alone pulls the signal down while the harness measures good