Home › Land Rover › 2021 › Defender 110 › Repair and Diagnosis › General Information › Specifications Index › Diagnostic Trouble Code Index DTC: Trailer Control Module (TRM) -- Defender/L663 › Diagnostic Trouble Code Index - DTC: Trailer Control Module (TRM) (G2445144) › Description And Operation › Trailer Control Module (TRM) › DTC B1548-23: Trailer Light Test Button - Signal stuck low › Possible Causes