For 1990-2009 cars

### Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor located in the lower coolant passage of the engine's cylinder head. When the coolant temperature is cold, the sensor has a high resistance. As the temperature increases, the resistance of the sensor decreases. The PCM provides a 5 volt signal to the coolant sensor, which is also connected to the PCM ground. The PCM reads the voltage drop on the signal line to determine coolant temperature.

### Conditions for Setting the DTC

DTC P0125 will set if the coolant temperature is below 0°C (32°F) after the engine has been running for more than 5 minutes when no ECT and IAT DTCs have been set.

Important: The ECT signal is continuously checked when the engine is running.

This DTC will only pass if the engine start was determined to be a cold start.

### Diagnostic Aids

DTC P0125 indicates lower than normal coolant temperatures and probably does not indicate a faulty ECT subsystem.

Possible causes of low coolant temperature:

• | Thermostat stuck open

• | Cooling fan always ON