The battery sensor which is embedded in the battery negative terminal transmits battery voltage and temperature information to the ECM. The ECM controls the alternator voltage output necessary for the various vehicle electric units by duty cycle based on signals received from the battery sensor. Also, on some vehicles with the ISG (idle stop & go) function, the idle stop and auto start are determined by the battery state of charge (SOC) and state of health (SOH) information received from the battery sensor. 

If an additional ground cable is installed, the battery sensor may incorrectly register that the battery is in a discharged state despite a normal battery condition. This may cause the battery sensor to transmit incorrect information to the ECM, alternator voltage output and ISG control, resulting in improper operation of various systems and components, as well as possible setting DTCs U1111 (battery sensor fault detected by ECM), U1112 (LIN communication error), P0620 (alternator control circuit), P2501 (AMS voltage rationality), P2502 (AMS charging system voltage), and/or P2503 (AMS no battery charge).