Home >> Land Rover >> 2021 >> Range Rover Base >> Repair and Diagnosis >> General Information >> Specifications Index >> Diagnostic Trouble Code Index DTC: Adaptive Speed Control Module (ASCM) -- Range Rover/L405 >> General Information >> Description And Operation >> Diagnostic Trouble Code Index - DTC: Adaptive Speed Control Module (ASCM) (G2391130) >> DTC C0078-61: Tire Diameter - Signal calculation failure >> Possible Causes