Engine Coolant Temperature (ECT) Sensor Circuit Low Input In simple terms, the ECU is seeing very low voltage from the coolant temperature sensor, which usually means the computer thinks the engine is extremely hot or the sensor circuit is shorted to ground. What the Coolant Temperature Sensor Does The ECT sensor tells the ECU the … Continue reading Code P0117 on a 2006 Dodge / Freightliner / Mercedes T1N Sprinter (2001–2006) means: