Diagnostic Aids

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Check for the following conditions:

A faulty thermostat that stays open slightly can cause DTC P0128 to set in cold weather when the vehicle is started and allowed to sit while warming up. Replace any suspect thermostat. Refer to THERMOSTAT REPLACEMENT (3.5L (L66)) .
An incorrect thermostat can cause the engine to warm up slowly. Replace any thermostat that does not meet OEM specifications..
Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted ECT sensor. A shifted sensor could result in DTC P0128. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor .
Check for the proper operation of the engine cooling system, including the correct coolant level.

If DTC P0128 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.