What does it mean?
B1258 is a Body (airbags, seat belts, body electronics) fault code. It indicates: AQS Sensor Short To Ground .
Symptoms
- Automatic recirculation never activates behind a smoky vehicle or in a tunnel
- Recirculation stays engaged permanently, so the cabin air becomes stuffy and the windows fog
- The air quality function cannot be switched on from the climate panel
- Exhaust and fuel odours reach the cabin that the system would normally block
- Heating and cooling otherwise work normally
Likely causes
- Sensor signal wire chafed and shorted to ground in the cowl or front harness
- Internally shorted sensing element inside the air quality sensor
- Water entering the sensor connector in the cowl area and bridging the pins
- Harness pinched when the cowl panel, wiper linkage, or air intake housing was reassembled
- Corroded terminals from long exposure to moisture at the fresh air intake
- Failed input circuit inside the climate control module
How to fix it
- Read the air quality sensor value in live data and see whether it is pinned at one end of its range
- Locate the sensor near the fresh air intake in the cowl area and inspect its connector for water and corrosion
- Unplug the sensor; if the code changes to an open circuit fault, the sensor itself is shorted
- With both ends disconnected, test the signal wire for continuity to ground
- Verify the supply voltage and ground at the sensor connector with the ignition on
- Repair the shorted harness section or replace the sensor, then clear the code and verify automatic recirculation works