Possible causes

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

When is the code detected?

The voltage sent to Engine Control Module (ECM) from the Engine Coolant Temperature (ECT) sensor is not practical, even when some time has passed after starting the engine. The engine is taking too long to reach the normal temperature level.

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

P0125 VOLKSWAGEN Description

The Engine Coolant Temperature (ECT) sensor is used to detect the engine coolant temperature. The sensor modifies a voltage signal from the Engine Control Module (ECM). The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases.