Home › Land Rover › 2021 › Defender 90 › Repair and Diagnosis › General Information › Specifications Index › Diagnostic Trouble Code Index DTC: Headlamp Control Module (HCM) -- Defender/L663 › Diagnostic Trouble Code Index - DTC: Headlamp Control Module (HCM) (G2423982) › Description And Operation › Headlamp Control Module (HCM) › DTC U201A-51: Control Module Main Calibration Data - Not programed › Possible Causes