2008 Honda Accord charging system The C circuit is responsible for controlling the charge mode. The voltage regulator sends a voltage to the ECM through the C circuit. Depending on the charging systems needs, the ECM either holds the voltage high to signal the high output mode, or it pulls the voltage low to signal the low output mode. When the circuit C voltage is pulled low by the ECM: the charging voltage at the battery will range from 12.4-12.9V. The ECM uses the low output mode when the engine is starting or if all of the following parameters are met: electrical Load below 15 Amps (varies with vehicle), vehicle speed between 10-45 mph or at idle while in drive, engine speed below 3,000 rpm, coolant temperature above 167°F (75°C), A/C Switch Off intake air temperature above 68°F (20°C).