Diagnostic Aids

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

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 resistance in wiring.
Skewed sensor. See TEMPERATURE VS RESISTANCE table under DTC P0117: ECT SENSOR CIRCUIT - LOW VOLTAGE/HIGH TEMPERATURE.