A6CF

The E90Post thread titled "Fault code for AUC Sensor - A6CF" treats it as the AUC sensor, and an owner there confirmed the code was stored in the JBE. A code library lists it under the junction box as "AUC sensor". Against them, an AutoExplain page says A6CF is a gear-ratio monitoring fault for sixth gear in an automatic transmission. The threads and the library agree with each other and not with that page, so this page follows them.

In the thread, the first owner fitted a sensor from a scrapyard and still got the code, noting that clearing codes with the sensor disconnected also throws A6CF. Later he wrote that he "had bad sensors" and a good one fixed it. He says he noticed no difference in use either way, describing the sensor as the one that recirculates air automatically when pollutant levels exceed a threshold. A second owner there, with an A/C that was not working, asked whether the AUC sensor could prevent the compressor from engaging and was told it will not prevent anything other than AUC-specific functions.

In another E90Post thread an owner whose A/C blower would not run had replaced the blower and its final stage and asked if A6CF could be the cause. A helper said no: no blower function means a blower wiring or activation problem, and asked for the fuse, voltage and ground readings at the blower connector. C90D60, the AUC sensor code on F-series cars, has its own page.