Electrical Load Signal (ECHO)

On vehicles equipped for cold areas, an input signal is delivered to ELS terminal of Engine Control Module (ECM) to indicate when high electrical output is required. This may occur when HTR SUB1 relay is energized to provide voltage to Positive Temperature Coefficient (PTC) heater. PTC heater is a small electrical heater located in the heater core. PTC heater will be turned on when engine coolant temperature is less than 176°F (80°C), engine speed is greater than 1050 RPM, generator power ratio is less than 95 percent and heater temperature control switch is positioned in maximum heat range. ECM may use input signal to maintain proper engine idle speed.