Home >> Jaguar >> 2015 >> XJR Base >> Repair and Diagnosis >> General Information >> DTC Index >> Diagnostic Trouble Code (DTC) Index DTC: TELEMATIC Control Module (TCU) -- XJ/X351 >> Diagnostic Trouble Code (DTC) Index DTC: Telematic Control Module (TCU) >> Description And Operation >> TELEMATIC Control Module (TCU) >> U2109-91 Back-up Battery - Parametric >> Possible Causes