C90D60

bmv.parts describes C90D60 as stored by the junction box for the AUC sensor, gives the BMW path as a junction box reset first and replacement of the sensor if the fault returns, and notes there is no drivability effect. The X3 thread quotes the fault entry as an internal fault of the automatic air recirculation control sensor, with supply voltage between 10.5 and 16 volts and terminal 15 on as its conditions.

In that X3 thread one owner removed the sensor, sanded each of its three pins with fine abrasive paper, refitted it and the error did not return, then sprayed the pins with silicone. Another cleaned the connector with MAF cleaner and dielectric grease and soaked the sensor in electronics cleaner. One poster says the sensor sits in the engine bay at the back right and is hard to remove without breaking the tab, that it drives the auto fresh/recirculation mode, and that you do not strictly need it (his is dead). Another notes that some owners who replaced the sensor still had the error. One poster, working down a list of codes, calls it the least important.