Home › Land Rover › 2021 › Defender 90 › Repair and Diagnosis › General Information › Specifications Index › Diagnostic Trouble Code Index DTC: TELEMATIC Control Unit Module (TCU) -- Defender/L663 › Diagnostic Trouble Code Index - DTC: TELEMATIC Control Unit Module (TCU) (G2400918) › Description And Operation › TELEMATIC Control Unit Module (TCU) › DTC U2109-09: Back-up Battery - Component failures › Possible Causes