For 1990-2009 cars

The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The powertrain control module (PCM) supplies a 5-volt reference through a pull-up resistor to the sensor, which is connected to ground. When the sensor is cold it has a high resistance (high signal voltage at PCM). As the sensor temperature increases, its resistance decreases (lower signal voltage at PCM). The PCM uses the signal voltage to determine engine coolant temperature. DTC P0125 sets when the engine coolant temperature has not reached the calibrated temperature necessary for closed loop fuel control.

### DTC Parameters

DTC P0125 will set if ECT sensor temperature is below 0°C (32°F) when:

• | The timer has been exceeded based on startup ECT.

• | The loop status is closed.

• | The startup ECT is between -40 and +44°C (-40 and +111°F)

• | No 5-volt reference, IAT, P0601 or P0606 DTCs have been set

DTC P0125 will pass only if PCM has determined engine start to be a cold start.

DTC P0125 runs continuously once the above conditions have been met.

DTC P0125 is a type B DTC.

### Diagnostic Aids

DTC P0125 indicates lower than normal engine coolant temperature which most likely was not caused by a short/open or intermittent short/open in the ECT wiring.

Possible causes of low engine coolant temperature:

• | Thermostat stuck open

• | Cooling fan always on

• | Very low ambient temperatures

• | Corrosion in connector or resistance in wiring

• | Skewed sensor

Refer to Engine Controls Component Descriptions for a Temperature versus Resistance chart.