It prevents the processor from shutting down when turning on vehicles featuring the start & stop system. When starting the engine, the vehicle battery voltage might decrease below 8 Volts value. If a signal processor (bit One, bit Ten) is installed in your system, especially with vehicles featuring the start & stop system, low supply voltage values might make the processor shut down. In order to avoid waiting for the processor to complete its turn-on cycle again, you can install the ES3 by connecting it in series to the processor power supply cables.