Technical Definition:

Engine Coolant Temperature (ECT) (Sensor 1) Circuit

Technical Description:

The ECT (Engine coolant temperature) sensor is basically a thermistor that changes resistance with temperature. Usually a two wire sensor, a 5Volt reference from PCM (Powertrain Control Module) and ground signal to PCM. This is different from a temperature SENDER (which usually operates the dash temperature gauge and operates in a similar way as the SENSOR, only it’s a different circuit than what a P0115 is referring to). As the temperature of the coolant changes, the resistance changes on the ground signal to the PCM. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. If the PCM detects a voltage condition that seems abnormally low or high,P0115 will set.

Possible Causes:

• Wiring or connector damaged at sensor
• Open or short in reference or signal circuit
• Open or short in signal circuit
• Bad PCM

Possible Symptoms:

• MIL (Malfunction Indicator Lamp) illumination will always occur
• Vehicle may be hard to start
• May blow a lot of black smoke and run extremely rich
• Engine may want to die or backfire in tailpipe
• Engine may run lean and increased Nox emissions may be apparent (Requires gas analyzer)
• Cooling fans may run all the time when they shouldn’t be, or not at all when they should be

Engine Coolant Temperature Circuit Malfunction

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Low engine coolant level
– Faulty Engine Coolant Temperature (ECT) sensor
– Faulty engine coolant thermostat
– Engine Coolant Temperature (ECT) sensor harness is open or shorted
– Engine Coolant Temperature (ECT) sensor circuit poor electrical connection

Specific Makes: