Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.