What does it mean?
B1259 is a Body (airbags, seat belts, body electronics) fault code. It indicates: AQS Sensor Fault .
Symptoms
- Automatic recirculation does not engage in traffic or when entering a tunnel
- The recirculation flap switches at random or stays closed all the time
- Exhaust and fuel odours come through the vents
- Windows fog up because recirculation stays selected too long
- The air quality function cannot be activated on the climate panel
Likely causes
- Sensing element contaminated or aged, so its output is no longer plausible
- Internal electronic failure inside the air quality sensor
- Sensor blocked by leaves, dust, or debris in the fresh air intake, preventing it from sampling outside air
- Poor supply voltage or a bad ground at the sensor connector
- Damaged or corroded wiring in the cowl area
- Fault in the climate module's air quality input circuit
How to fix it
- Check the sensor's live value and see whether it reacts to a deliberate source of fumes
- Clear leaves and debris from the cowl and fresh air intake so the sensor can sample properly
- Inspect the sensor connector for corrosion and confirm supply voltage and ground with the ignition on
- Check the wiring between the sensor and the climate module for damage in the cowl area
- Replace the air quality sensor if the supply and wiring are good but its output never changes
- Clear the code and confirm that automatic recirculation reacts during a road test