What does it mean?
The humidity sensor returns a voltage proportional to the moisture content of the intake air, and the module knows the highest voltage a working sensor is capable of sending. This code is stored when the signal stays above that ceiling, close to reference voltage, for longer than the calibrated period. An open signal wire or an open sensor ground allows the module input to float up toward reference through its internal pull-up, so a missing connection often looks the same as a short to a voltage supply. While the code is active the module discards the reading and works from a default humidity figure.
Symptoms
- MIL on with humidity displayed at maximum or at an obviously fixed value
- Protective spark and boost calibration reducing throttle response
- On diesels, altered EGR flow and sometimes additional smoke
- Slight increase in consumption
- In many cases no other driveability change, which leaves the lamp as the main clue
- The fault reappearing after a code clear as soon as the engine runs
Likely causes
- Open circuit in the signal wire between the sensor and the module
- Open or high resistance sensor ground circuit
- Signal wire shorted to a battery voltage feed running in the same harness
- Connector not fully seated or a terminal backed out of its housing
- Internally open sensing element
- Corrosion at the sensor pins creating a high resistance path that behaves like an open
- Rarely, an internal module fault holding the input high
How to fix it
- Verify the live signal is genuinely at the high limit and review the freeze frame conditions
- Jump the signal terminal to ground at the sensor connector with the key on; if the reading falls to the low limit, the harness and module input are good and the sensor is suspect
- Measure the sensor ground circuit for continuity and voltage drop back to its ground point
- Check continuity of the signal wire from sensor to module connector while flexing the harness
- Test for battery voltage on the signal wire with the sensor unplugged to find a short to power
- Repair the open or shorted conductor, reseat or renew damaged terminals and seal the connector
- Replace the sensor when the wiring checks good and the element itself is open