P0128

Wiring Diagram:

P0128- ECT BELOW THERMOSTAT REGULATING TEMPERATURE
The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The ECM supplies a five 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 ECM). As the sensor temperature increases, its resistance decreases (lower signal voltage at ECM). The ECM uses the signal voltage to determine engine coolant temperature. DTC P0128 will set when the engine coolant temperature is consistently a certain temperature lower than the predicated engine coolant temperature during certain engine accumulated airflow stages. This DTC indicates that the engine is running cooler than normal.

DTC PARAMETERS
DTC P0128 will set if the ECT is 10.5°C (51°F) lower than normal based on predicted measurements after a set of calculated accumulated engine airflow stages have passed when:
^ Start-up ECT is between -7.5 and 50°C (19 and 122°F)
^ Start-up IAT is between -30 and 450°C (-22 and 113°F)
^ ECT is less than 84°C (183°F)
^ At least 3 kg of air has passed through the engine
^ Vehicle speed is present

DTC P0128 runs continuously once the above conditions have been met.

DTC P0128 is a type B DTC

DIAGNOSTIC AIDS
DTC P0128 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 fans always On
^ Very low ambient temperatures
^ Corrosion in connector or res1stance in wiring
^ Skewed ECT sensor

Refer to ECT General Description for a Temperature vs. Resistance chart.