Home >> Land Rover >> 2017 >> Range Rover Autobiography >> Repair and Diagnosis >> Accessories & Equipment >> Communication Devices >> Diagnostic Trouble Code Index DTC: Telematics Control Module (TCU) -- Range Rover/L405 >> Diagnostic Trouble Code Index DTC: Telematics Control Module (TCU) >> Description And Operation >> DTC U2109-91: Back-up Battery - Parametric >> Possible Causes