What does it mean?
B1281 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Air Conditioner > Humidity Sensor Short (Low) – AUTO Defog .
Symptoms
- Automatic defog no longer activates, the windscreen fogs up and stays fogged
- A/C compressor either runs constantly in AUTO mode or never engages for dehumidification
- Climate system falls back to a fixed default strategy and ignores cabin humidity
- Fault indication on the climate display
- Heating and blower still work, engine operation is unaffected
Likely causes
- Sensor signal wire shorted to ground inside the headliner or windscreen area harness
- Sensor failed internally and its output is pulled low
- Sensor element contaminated with dust, film or condensation, it sits against the glass near the mirror mount
- Corroded or loose terminals in the sensor connector
- Sensor damaged or left unplugged during windscreen or mirror pod replacement
- Missing 5V reference feed, so the signal sits at the minimum value
- Climate control module input circuit failure
How to fix it
- Look at the humidity and windscreen temperature values in live data; a reading stuck at zero or minimum points to a low short
- Unplug the sensor and check whether the signal line rises; if it stays low the harness is shorted to ground
- Inspect the sensor connector and the harness routed behind the mirror pod and headliner for pinching
- Measure the reference voltage and the ground at the sensor connector with a multimeter
- Clean the sensor area and confirm the sensor sits correctly against the glass with its foam gasket intact
- Replace the humidity sensor if reference voltage and wiring test correct
- Configure or relearn the climate module if the replacement sensor requires it, then clear codes and verify AUTO defog operation