Home >> Land Rover >> 2021 >> Defender 90 >> Repair and Diagnosis >> General Information >> Specifications Index >> Diagnostic Trouble Code Index DTC: Tow Bar Control Module (TBM) -- Defender/L663 >> Diagnostic Trouble Code Index - DTC: Tow Bar Control Module (TBM) (G2400887) >> Description And Operation >> Tow Bar Control Module (TBM) >> DTC B1548-23: Trailer Light Test Button - Signal stuck low >> Possible Causes