Home >> Land Rover >> 2017 >> Discovery Sport SE >> Repair and Diagnosis >> Quick Lookups >> DTC Index >> Diagnostic Trouble Code Index DTC: Automatic Temperature Control Module (ATCM) -- Discovery Sport/L550 >> Diagnostic Trouble Code Index DTC: Automatic Temperature Control Module (ATCM) >> Description And Operation >> DTC B12B9-4B: Auxiliary Heater Control Module - Over temperature >> Possible Causes